Laser irradiation apparatus, laser irradiation method, and method for manufacturing a semiconductor device

ABSTRACT

YAG laser can simultaneously emit a plurality of laser beams having different wavelengths from each other. By simultaneously irradiating the laser beams having different wavelengths from each other to a same region of a non-single crystal semiconductor film, an interference influence is suppressed to obtain a more uniform laser beam. For example, by simultaneously generating second and third harmonics of YAG laser to irradiate the same region through suitable optical system, a laser beam having higher uniformity and having an energy in which interference is highly suppressed is obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for manufacturing asemiconductor device having a circuit structured with a thin filmtransistor. For example, the invention relates to an apparatus formanufacturing an electro-optical device, typically a liquid crystaldisplay device, and the structure of electric equipment mounted withsuch an electro-optical device as a component. Note that throughout thisspecification, the semiconductor device indicates general devices thatmay function by use of semiconductor characteristics, and that the aboveelectro-optical device and electric equipment are categorized as thesemiconductor device.

2. Description of the Related Art

In recent years, the technique of crystallizing and improving thecrystallinity of an amorphous semiconductor film or a crystallinesemiconductor film (a semiconductor film having a crystallinity which ispolycrystalline or microcrystalline, but is not a single crystal), inother words, a non-single crystal semiconductor film, formed on aninsulating substrate such as a glass substrate by laser annealing, hasbeen widely researched. Silicon film is often used as the abovesemiconductor film.

Comparing a glass substrate with a quartz substrate, which is often usedconventionally, the glass substrate has advantages of low-cost and greatworkability, and can be easily formed into a large surface areasubstrate. This is why the above research is performed. Also, the reasonfor preferably using a laser for crystallization resides in that themelting point of a glass substrate is low. The laser is capable ofimparting high energy only to the non-single crystalline film withoutcausing much change in the temperature of the substrate.

The crystalline silicon film is formed from many crystal grains.Therefore, it is called a polycrystalline silicon film or apolycrystalline semiconductor film. A crystalline silicon film formed bylaser annealing has high mobility. Accordingly, it is actively used in,for example, monolithic type liquid crystal electro-optical deviceswhere thin film transistors (TFTs) are formed using this crystallinesilicon film and used as TFTs for driving pixels and driving circuitsformed on one glass substrate.

Furthermore, a method of performing laser annealing is one in which alaser beam emitted from a pulse oscillation type excimer laser, which islarge in output, is processed by an optical system so that the laserbeam thereof becomes a linear shape that is 10 cm long or greater or asquare spot that is several cm square at an irradiated surface tothereby scan the laser beam (or relatively move the irradiation positionof the laser beam to the irradiated surface). Because this method ishigh in productivity and industrially excellent, it is being preferablyemployed. A laser beam that has been linearized into a laser beam thatis 10 cm long or greater at the irradiated surface is referred as alinear laser beam throughout the present specification.

Different from when using a spot shape (square) laser beam whichrequires a front, back, left, and right scan, when using the linearlaser beam, in particular, the entire irradiated surface can beirradiated by the laser beam which requires only scanning at a rightangle direction to the linear direction of the linear laser beam,resulting in the attainment of a high productivity. To scan in adirection at a right angle to the linear direction is the most effectivescanning direction. Because a high productivity can be obtained, usingthe laser beam that is emitted from the pulse oscillation type excimerlaser and processing it into a linear laser beam by an appropriateoptical system for laser annealing at present is becoming a mainstream.

Shown in FIGS. 1A and 1B is an example of the structure of an opticalsystem for linearizing the sectional shape of a laser beam on theirradiated surface. This structure is a very general one and allaforementioned optical systems conform to the structure of the opticalsystem shown in FIGS. 1A to 1B. This structure of the optical system notonly transforms the sectional shape of the laser beam into a linearshape, but also homogenizes the energy of the laser beam in theirradiated surface at the same time. Generally, an optical system thathomogenizes the energy of a beam is referred to as a beam homogenizer.

If the excimer laser, which is ultraviolet light, is used as the lightsource, then the core of the above-mentioned optical system may be madeof, for example, entirely quartz. The reason for using quartz resides inthat a high transmittance can be obtained. Further, it is appropriate touse a coating in which a 99% or more transmittance can be obtained withrespect to a wavelength of the excimer laser that is used.

The side view of FIG. 1A will be explained first. Laser beam emittedfrom a laser oscillator 101 is split at a right angle direction to theadvancing direction of the laser beam by cylindrical lens arrays 102 aand 102 b. The right angle direction is referred to as a longitudinaldirection throughout the present specification. When a mirror is placedalong the optical system, the laser beams in the longitudinal directionwill curve in the direction of light curved by the mirror. These laserbeams in this structure are split into 4 beams. The split laser beamsare then converged into 1 beam by a cylindrical lens 104. Then, theconverged laser beam are split again and reflected at a mirror 107.Thereafter, the split laser beams are again converged into 1 beam at anirradiated surface 109 by a doublet cylindrical lens 108. A doubletcylindrical lens is a lens that is constructed of 2 pieces ofcylindrical lenses. Thus, the energy in the width direction of thelinear laser beam is homogenized and the length of the width directionof the linear laser beam is also determined.

The top view of FIG. 1B will be explained next. Laser beam emitted fromthe laser oscillator 101 is split at a right angle direction to theadvancing direction of the laser beam and at a right angle direction tothe longitudinal direction by a cylindrical lens array 103. The rightangle direction is called a vertical direction throughout the presentspecification. When a mirror is placed along the optical system, thelaser beams in the vertical direction will curve in the direction oflight curved by the mirror. The laser beams in this structure is splitinto 7 beams. Thereafter, the split laser beams are converged into 1beam at the irradiated surface 109 by the cylindrical lens 104. Thus,homogenization of the energy in the longitudinal direction of the linearlaser beam is made and the length of the longitudinal direction is alsodetermined.

The above lenses in the optical system are made of synthetic quartz forcorrespondence to excimer laser. Furthermore, coating is implemented onthe surfaces of the lenses so that the excimer laser will be welltransmitted. Therefore, the transmittance of excimer laser through onelens is 99% or more.

By irradiating the linear laser beam linearized by the above structureof the optical system in an overlapping manner with a gradual shift inthe width direction thereof, laser annealing is implemented to theentire surface of a non-single crystal silicon film to therebycrystallize the non-single crystal silicon film and thus itscrystallinity can be enhanced.

A typical method of manufacturing a semiconductor film that is to becomethe object to be irradiated is shown next.

First, a 5 inch square Corning 1737 substrate having a thickness of 0.7mm is prepared as the substrate. Then a 200 nm-thick SiO₂ film (siliconoxide film) is formed on the substrate and a 50 nm-thick amorphoussilicon film (hereinafter denoted by “a-Si film”) is formed on thesurface of the SiO₂ film. Both films are formed by employing the plasmaCVD apparatus.

The substrate is exposed under an atmosphere containing nitrogen gas ata temperature of 500° C. for 1 hour to thereby reduce the hydrogenconcentration in the film. Accordingly, the laser resistance in the filmis remarkably improved.

The XeCl excimer laser L3308 (wavelength: 308 nm, pulse width: 30 ns)manufactured by Lambda Co. is used as the laser apparatus. This laserapparatus generates a pulse oscillation laser and has the ability tooutput an energy of 500 mJ/pulse. The size of the laser beam at the exitof the laser beam is 10×30 mm (both half-width). Throughout the presentspecification, the exit of the laser beam is defined as theperpendicular plane in the advancing direction of the laser beamimmediately after the laser beam is emitted from the laser irradiationapparatus.

The shape of the laser beam generated by the excimer laser is generallyrectangular and is expressed by an aspect ratio which falls under therange of the order of 2 to 5. The intensity of the laser beam growsstronger towards the center of the beam and indicates the Gaussiandistribution. The size of the laser beam processed by the optical systemhaving the structure shown in FIG. 1 is transformed into a 125 mm×0.4 mmlinear laser beam having a uniform energy distribution.

Based upon an experiment conducted by the present inventor, whenirradiating a laser to the above-mentioned semiconductor film, the mostsuitable overlapping pitch is approximately 1/10 of the width(half-width) of the linear laser beam. The uniformity of thecrystallinity in the film is thus improved. In the above example, thehalf-width of the linear laser beam was 0.4 mm, and therefore the pulsefrequency of the excimer laser was set to 30 hertz and the scanningspeed was set to 1.0 mm/s to thereby irradiate the laser beam. At thispoint, the energy density in the irradiated surface of the laser beamwas set to 420 mJ/cm². The method described so far is a very generalmethod employed for crystallizing a semiconductor film by using a linearlaser beam.

When an extremely attentive observation is made to a silicon film thathas been laser annealed by using the above-mentioned linear laser beam,very faint interference patterns were seen in the film. The cause of theinterference patterns seen in the film resides in that the laser beam issplit and assembled in 1 region, and therefore the split light bringsabout interference with each other. However, because the coherent lengthof the excimer laser is about several microns to several tenths ofmicrons, a strong interference will not occur. As a result, theinfluence imparted by the above-mentioned interference to asemiconductor device is extremely small.

The excimer laser is large in output and capable of oscillating pulsesrepetitively at a high frequency (approximately 300 hertz under thepresent situation), and hence is often used in performingcrystallization of a semiconductor film. In recent years, advances havebeen made in manufacturing, low temperature poly-silicon TFTs used inliquid crystal displays. Accordingly, the excimer laser is employed inthe crystallization process of semiconductor films.

Further, the largest output of an YAG laser is remarkably improved.Because the YAG laser is a solid state laser, it is easier to handle andmaintain compared with the excimer laser which is a gas laser.Therefore, in the crystallization process of a semiconductor film, ifthe YAG laser is substituted for the excimer laser, an astoundingimprovement in cost performance can be expected. On the basis of thebackground such as the above, the present applicant is makingan-examination in the possibility of using the YAG laser in thecrystallization process of a semiconductor film.

It is known that the YAG laser outputs a laser beam having a wavelengthof 1065 nm as the fundamental wave. The absorption coefficient of thislaser beam with respect to silicon films is extremely low, and thereforethe laser beam as it is cannot be used in the crystallization process ofthe a-Si film, which is one of the silicon films. However, the laserbeam, i.e., the fundamental wave, can be modulated into having a shorterwavelength by using a non-linear optical crystal. Due to the modulatedwavelengths, the laser beam is named a second harmonic (wavelength 533nm), a third harmonic (wavelength 355 nm), a fourth harmonic (wavelength266 nm), and a fifth harmonic (wavelength 213 nm).

Since the wavelength of the second harmonic is 533 nm, it has sufficientabsorption to an a-Si film that is about 50 nm thick, and hence can beused in crystallizing the a-Si film. In addition, the third harmonic,the fourth harmonic, and the fifth harmonic also have a high absorptionto the above-mentioned a-Si film, and therefore similar crystallizationcan be performed.

The largest output of the second harmonic from the currentgeneral-purpose YAG laser is about 1500 mJ/pulse. Further, the largestoutput of the third harmonic thereof is about 750 mJ/pulse and thelargest output of the fourth harmonic thereof is about 200 mJ/pulse. Thelargest output of the fifth harmonic is further lower than theaforementioned largest outputs, and thus if the fifth harmonic is usedin crystallizing the a-Si film, mass production will become extremelyworse. Taking into consideration both the output of the laser beam andits absorption to the a-Si film, at the present level, it is best to usethe second harmonic and the third harmonic.

In the case of using the YAG laser to crystallize the semiconductorfilm, nonetheless, the shape of the laser beam at the irradiated surfaceis preferably linear for mass production. Hereinbelow, an examination ismade on the possibility of applying the above-mentioned optical systemto the YAG laser without any modifications made thereto.

First, the difference between the beam shape of the YAG laser and thebeam shape of the excimer laser will be described. The shape of thelaser beam emitted from the excimer laser is generally rectangular,whereas the shape of the laser beam emitted from the YAG laser is bothcircular and rectangular. To process a rectangular laser beam into alinear laser beam is comparatively easy since transformation is madefrom a rectangular shape to a rectangular shape. However, to transform acircular beam into a rectangular linear laser beam is comparativelydifficult. Therefore, judging from the shape of the beam only, it isbetter to use the rectangular beam emitted from the YAG laser than touse the circular beam emitted therefrom.

Hereinafter, a description will be made on the uniformity of energybetween the beam of the YAG laser which emits the rectangular beam andthe beam of the YAG laser which emits the circular beam, and anexamination is conducted to discern which one of the YAG lasers issuitable as a substitute for the excimer laser.

The type of YAG laser which has a beam shape that is circular irradiatesa strong light (flash lamp and laser diode, hereinafter denoted by LD)for exciting a cylindrical crystal rod, thereby obtaining laseroscillation. On the other hand, the type of YAG laser which has a beamshape that is rectangular irradiates a strong light to a parallelepipedcrystal rod that structures a system called a zigzag slab, therebyobtaining laser oscillation.

Comparing the energy uniformity of the beam oscillated from the YAGlaser which has a beam shape that is circular with that of the excimerlaser, the energy uniformity of the former is in general not good. Thisnon-uniformity of energy originates from a temperature distribution ofthe above-mentioned cylindrical crystal rod which occurs from theapplication of a strong light. As can be readily surmised from the shapeof the aforementioned cylindrical crystal rode, the temperature of thetemperature distribution thereof becomes lower towards the exterior ofthe cylinder. Thus, a function similar to that of a lens is added to theaforementioned cylindrical crystal rod, thereby worsening the energyuniformity of the beam. This phenomenon is generally called the thermallens effect.

A system conceived for the purpose of restraining the above thermal lenseffect is a zigzag slab system of the YAG laser. The structure of thezigzag slab system of the YAG laser will be briefly explained withreference to FIG. 2 in the following.

The rod system YAG laser obtains laser oscillation by excitation of thecylindrical crystal called a crystal rod. However, in the case of thezigzag slab system YAG laser, the shape of the crystal rod isparallelepiped. A parallelepiped crystal 202 is irradiated by excitationlamps 203 a and 203 b, for example, an LD and a flash lamp, to therebyobtain laser oscillation. Electric power is supplied to the excitationlamps 203 a and 203 b from a power source 208. Furthermore, theparallelepiped crystal 202 is cooled by a cooler 207.

Arranging resonant mirrors 201 and 204 diagonally to the parallelepipedcrystal 202 is a characteristic of the zigzag slab system. The resonantmirrors 201 and 204 are arranged parallel in a state facing each otherand sandwiching the parallelepiped crystal 202. Each of the surfaces ofthe parallelepiped crystal 202 and the resonant mirrors has no parallelpositional relationship. By appropriately adjusting the positionalrelationship, light reflected from the resonant mirrors will advance ina zigzag way within the parallelepiped crystal. When laser is oscillatedat this point in this state, a large amount of light will exit from aside surface of the parallelepiped crystal resulting in a large lost ofenergy, and thus becoming unusable. In order to prevent this drawback,reflector mirrors 205 and 206 are arranged at the side surfaces of theparallelepiped crystal to thereby prevent light escaping from theparallelepiped crystal 202. Gold-plated mirrors, for example, may beused as the reflector mirrors 205 and 206.

By adopting the above structure, the laser beam not only passes throughthe interior portion of the parallelepiped crystal rod, but also passesthrough the exterior portion thereof. Thus, influence to the biasedlaser beam of the temperature distribution of the crystal is less thanthe case of using the cylindrical crystal rod. Consequently, influencefrom the thermal lens effect becomes lesser thereby enhancing theuniformity of the beam.

Thus, it can be determined from the above examination that the zigzagsystem YAG laser is suitable as a substitute for the excimer laser thanthe type of YAG laser which employs the cylindrical crystal rod becausethe shape of the laser beam emitted from the zigzag system YAG laser issimilar to that of the excimer laser and the uniformity of the beamthereof is higher.

Next, consideration is made in regards to a difference in the coherentlength of the YAG laser and the excimer laser. As stated above, thecoherent length of the excimer laser is about several microns to severaltenths of microns, and therefore the occurrence of light interferencewhen the laser beam passes through the aforementioned optical system,which splits and then converges the laser beam into 1 beam again, isthus very weak. On the other hand, the coherent length of the YAG laseris quite long, about 1 cm or more. Hence, the influences of theinterference due to this long coherent length of the YAG laser cannot beignored.

If the laser beam emitted from the YAG laser is passed through theoptical system shown in FIG. 1 to be processed into a linear laser beam,then a linear laser beam 300 having an energy distribution withrepetitive strong and weak regions in a lattice pattern as shown in FIG.3A is formed.

The lattice pattern energy distribution is caused by the lightinterference. In FIG. 3A, darker lines 301 denotes regions where theenergy is comparatively high and blank lines 302 between the darkerlines 301 denotes regions where the energy is comparatively low.

Using the linear laser beam 300, which has a lattice pattern energydistribution, to crystallize the a-Si film will nonetheless causenon-uniform crystallization in the surface of the a-Si film. Shown inFIG. 3B is the appearance of a front surface of a silicon film 303crystallized by the linear laser beam. As described in the above, thelinear laser beam is irradiated on the a-Si film in the width directionof the linear laser beam and overlaps each other in a manner that isabout 1/10 of the length of the width of the laser beam. Therefore, thestripes parallel to the linear direction of the linear laser beameliminate each other out, becoming inconspicuous. However, lines 304 and305 that are parallel to the width direction of the laser beam stronglyremain. In FIG. 3B, darker lines 304 denotes regions where the energy iscomparatively high and blank lines 305 between the darker lines 304denotes regions where the energy is comparatively low.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and thereforehas an object thereof to select an appropriate YAG laser as a substitutefor an excimer laser used for the crystallization of a semiconductorfilm, and to resolve the aforementioned problem of an interferencepattern, thereby providing a laser irradiation apparatus for attaining apolycrystalline silicon film having very little stripe patterns.

The inventors of the present invention have selected a zigzag slabsystem YAG laser, which has a rectangular beam shape, as the appropriateYAG laser for employment in the crystallization of a semiconductor film.In the present invention, it is important that the shape of the beam isrectangular, and there is no particular problem in using a YAG laser ofa different system. However, the present inventor considers the zigzagslab system as the most suitable system among the current systems of theYAG laser at present. Further, the laser irradiation apparatus disclosedin the present specification is not particularly limited to one thatemits a rectangular laser beam, but a laser irradiation apparatus thatemits a circular laser beam may also be used.

As a problem that occurs when the YAG laser is used in crystallizing thesemiconductor film is that interference, as mentioned in the aboveparagraph, is liable to occur in the YAG laser compared with the excimerlaser.

The present invention will provide a technique to suppress an influenceof the interference pattern. As mentioned before, the oscillationwavelength of the YAG laser includes a fundamental wave (1.06 um), asecond harmonic (0.53 um), a third harmonic (0.35 um), a fourthharmonic, a fifth harmonic, and so forth.

Shown in FIG. 4A is a schematic view of a simplified beam homogenizerhaving the second harmonic of the YAG laser as a light source. Afundamental wave emitted from a light source 401 is converted into thesecond harmonic by a non-linear optical element 402. Because componentsof the fundamental wave still remain in the laser beam converted intothe second harmonic, at a beam splitter 403, only the fundamental waveis transmitted and the second harmonic is reflected. Next, the lightpath of the second harmonic is bend 90 degrees by a mirror 404, and thensplit into 2 beams by a cylindrical lens array 405. Thereafter, thesplit beams are converged into 1 beam at an irradiated surface 407 by acylindrical lens 406. At the irradiated surface 407 at this point,lights having equivalent wavelengths advance in opposite directions toeach other, thereby interfering with each other. The pattern ofinterference that has developed in the irradiated surface 407 is shownin FIG. 4B. The pattern of interference illustrated in FIG. 4B is one inwhich plural patterns of wave shapes that change with time areoverlapped. Throughout the present specification, a plural number ofpatterns of interference are shown, but all will be shown in the samemethod as that of FIG. 4B.

A stationary wave is formed when lights of equivalent wavelengthsadvance in opposite direction from each other. However, in a portionwhere energy is weak, the energy thereof becomes extremely weak. Thus,when a region having an immense energy difference is formed, a massivedecline in the uniformity of crystallization by using laser is thereforeunavoidable.

Accordingly, by utilizing the characteristic of the YAG laser capable ofsimultaneously emitting plural kinds of wavelengths of light, thepresent inventor designed a method of making the interference patterninconspicuous by compositing YAG lasers of different wavelengths.

An example of a system that is capable of making the interferencepattern inconspicuous is shown in FIG. 5A. Light (fundamental wave)oscillated from a resonator 501 of the YAG laser is converted into thesecond and third harmonic, besides being converted to the fundamentalwave, via a non-linear crystal 502 for converting wavelengths. Thefundamental wave is split by a beam splitter 503 which is provided withfunctions to satisfactorily penetrate the wavelength region of thefundamental wave, and to satisfactorily reflect the other wavelengths.Lights having the second and third harmonic reflected from the beamsplitter 503 intermingled can thus be formed. Then at a beam splitter504, only the second harmonic is reflected while the third harmonic istransmitted. Finally, the advancing direction of the third harmonic isalternated by a reflector mirror 505 so that the advancing directionthereof is the same as the advancing direction of the second harmonic.

Thus, a YAG laser capable of simultaneously emitting 3 types of lights,that is, the fundamental wave, the second harmonic, and the thirdharmonic, can be made through the above structure. Not much of thefundamental wave is absorbed by the silicon film, and hence is not usedin the crystallization of the silicon film. The second and thirdharmonic are used in the crystallization thereof.

Shown in FIG. 34 is a wavelength dependence of a ratio of the absorptionof light to a 55 nm-thick a-Si film formed on a glass substrate. As canbe known from the graph, when light having a wavelength of 600 nm orless is used, there is a 10 percent or more absorption to the siliconfilm. Therefore, when the present invention is applied to a 55 nm-thicka-Si film, light having a wavelength of 600 nm or less is used.

The second harmonic is split into 2 beams by a cylindrical lens array506. On the other hand, the third harmonic is split into 2 beams by acylindrical lens array 507. The cylindrical lens arrays 506 and 507 areset at positions with equivalent focal lengths. Finally, a cylindricallens 508 is arranged and the laser beam which has been split into 4beams are composited to 1 region by the cylindrical lens 508.

The second harmonic and the third harmonic enter the cylindrical lens508. Therefore, though there is a few percentage of difference in thefocal length to the second harmonic and the third harmonic with eachother, there is no influence to the present experiment. Quartz, whichhas a high transmissivity to both the second harmonic and the thirdharmonic, is used as the material of the lenses. Interference occurs inan irradiated surface 509 due to the fact that the second harmonic andthe third harmonic advance in opposite directions from each other. Asimulation result of the pattern of interference formed in theirradiated surface 509 is shown in FIG. 5B. It is apparent from thegraph of FIG. 5B that nodes caused by the interference have disappeared.

FIG. 6 is a view illustrating the state of an interference that hasoccurred when the second harmonic and the third harmonic havingequivalent swinging widths with each other are made to advance inopposite directions from each other at equivalent speeds. In FIG. 6, thelongitudinal axis denotes the intensity of light and the lateral axisdenotes a position. As can be understood from FIG. 6, it is apparentthat the energy distribution of light is more balanced in this case thanin the case of using only the second harmonic.

An output of the second harmonic emitted from the YAG laser having thestructure of FIG. 5 is about twice the size of an output of the thirdharmonic. Therefore, in order to synthesize the second harmonic and thethird harmonic emitted from the YAG laser having the structure of FIG. 5to thereby make the interference patterns inconspicuous, it is necessaryto consider synthesizing a second harmonic that has a swinging width of√{square root over ( )}2 and a third harmonic that has a swinging widthof 1. The simulation result thereof is shown in FIG. 7. Making theswinging width of the second harmonic of FIG. 6 to √{square root over ()}2 times is the result of FIG. 7. Similar to the result of FIG. 6, theenergy distribution of light is also satisfactorily balanced in FIG. 7.

Thus, from the above results, it can be surmised that the contrast of astrong and weak pattern of the energy caused by the interference can beeasily suppressed by synthesizing lights having different wavelengthsfrom each other. Actually, similar results can be expected fromsynthesizing the second harmonic and the fourth harmonic andsynthesizing the third harmonic and the fourth harmonic. An example ofsynthesizing the second harmonic and the fourth harmonic is shown inFIG. 8, and an example of synthesizing the third harmonic and the fourthharmonic is shown in FIG. 9. It is apparent that the energy is madeuniform in both examples. Energy uniformity can also be achieved even if3 types or more different wavelengths of laser beams are mixed together.In other words, by irradiating each of the laser beams having differentwavelengths from each other to the same region and at the same time,uniformity of the laser beam in the same region can be improved.

The above-mentioned method of making the interference patterninconspicuous by synthesizing laser beams of different wavelengths isapplied to the optical system for forming linear laser beams that isillustrated in FIG. 1. The interference pattern is made inconspicuous bymaking laser beams of different wavelengths advance in oppositedirections from each other at equivalent speeds. For example, the effectof making the interference pattern inconspicuous can be obtained in anoptical system for forming linear laser beams illustrated in FIG. 10.The optical system shown in FIG. 10 is a beam homogenizer, similar tothe optical system shown in FIG. 1. The basic perspective ofconstructing the lenses in both optical systems is the same.

The role of the optical system structured as shown in FIG. 10 will beexplained. The aforementioned YAG laser is used as a laser oscillator.The YAG laser oscillates the second harmonic and the third harmonic inaddition to the fundamental wave. The fundamental wave outputted from alaser resonator 1001 is converted into the second harmonic and the thirdharmonic by a non-linear optical element 1002. Components of thefundamental wave remain in the second harmonic and the third harmonic.Next, the fundamental wave is separated by a beam splitter 1003 whilethe second harmonic and the third harmonic are introduced to a beamsplitter 1004. The second harmonic and the third harmonic are furtherseparated into a second harmonic and a third harmonic by the beamsplitter 1004.

Penetrating the beam splitter 1004, the advancing direction of the thirdharmonic is bent by reflector mirrors 1005 and 1006. As a result, thesecond harmonic and the third harmonic exit at oblique opposite anglepositions in the form of being parallel with each other.

The second harmonic is first split into 2 beams in the verticaldirection by a cylindrical lens array 10071, and then split into 2 beamsin the horizontal direction by a cylindrical lens array 10081. Thesesplit laser beams are converged into 1 beam at an irradiated surface1011 by cylindrical lenses 10091 and 10101.

On the other hand, the third harmonic is first split into 2 beams in thevertical direction by cylindrical lens array 10072, and then split into2 beams in the horizontal direction by a cylindrical lens array 10082.These split beams are converged into 1 beam at the irradiated surface1011 by cylindrical lenses 10092 and 10102.

The reason why the structure of FIG. 10 is able to make the interferencepattern become inconspicuous will be explained with reference to FIG.11. FIG. 11 is a top view of the optical system of FIG. 10. The laserbeam split into 4 laser beams and converged into 1 beam in thelongitudinal direction of the linear laser beam are denoted by thefollowing names, respectively: laser beam A (the laser beam that passesthe outermost right-hand side), laser beam B (the laser beam that passesthe inner side of the right-hand side), laser beam C (the laser beamthat passes the inner side of the left-hand side), and laser D (thelaser beam that passes the outermost left-hand side).

Laser beam A is the third harmonic and laser beam D is the secondharmonic. Both laser beams are advancing in opposite directions fromeach other at equivalent speeds, and therefore the effect of making theinterference pattern in the irradiated surface 1011 inconspicuous isattained. Laser beam B is the third harmonic and laser beam C is thesecond harmonic. Both laser beams are advancing in opposite directionsfrom each other at equivalent speeds, thereby attaining the effect ofmaking the interference pattern in the irradiated surface 1011inconspicuous. That is, laser beam A and laser beam D erase aninterference effect with each other. Furthermore, laser beam B and laserbeam C erase an interference effect with each other.

Shown in FIG. 12A is the state of an interference in the irradiatedsurface 1011, which is calculated by a computer, when the laser beams inFIG. 11 are all second harmonic. In this graph, it is apparent that theformation of loops and nodes are distinctive due to the influence ofinterference. On the other hand, shown in FIG. 12B is the state of aninterference in the irradiated surface 1011 when the above method isadopted in the optical system of FIG. 11. The loops and nodes that wereseen in FIG. 12A have disappeared, and hence it is discerned that theenergy has been made uniform. The essence of the present invention is inmaking each of the lights having different wavelengths uniform and thensynthesizing the respective uniform lights into 1 light in theirradiated surface.

Accordingly, the possible stripe pattern developing in the semiconductorfilm when the semiconductor film is laser annealed with a YAG laser thathas been processed into a linear laser beam can thus be madeunnoticeable. Although cited in the present specification is an exampleof taking out laser beams having different wavelengths from each otherfrom 1 laser oscillator, there is no influence of any kind inflictedupon the essence of the present invention even if laser beams havingdifferent wavelengths from each other are taken out from 2 laseroscillators. In this case, a trigger is tuned in to so that the emissionof lasers having different wavelengths from each other may be performedat the same time. The present invention is not limited to the YAG laserbut can be applied to all laser irradiation apparatuses having a longcoherent length such as a glass laser and an Ar laser. In addition, thepresent invention is not limited to a linear laser beam that has alinear section in the irradiated surface but is also applicable to arectangular laser beam having a small aspect ratio. The presentinvention is further applicable to a square shape laser beam.

That is, according to the present invention, there is provided a laserirradiation apparatus that irradiates a laser beam with a section whichbecomes linear, square-like, or rectangular in an irradiated surface,characterized by comprising a laser oscillator that emits a plurality oflaser beams having different wavelengths from each other, an opticalsystem for processing the plurality of sectional laser beams havingdifferent wavelengths from each other into a square-like or rectangularlaser beam in the irradiated surface, respectively, and making an energydistribution uniform, and a stage for arranging an object to beirradiated.

According to another aspect of the present invention, there is provideda laser irradiation apparatus that irradiates a laser beam with asection which becomes linear in an irradiated surface, characterized bycomprising a laser oscillator that emits a plurality of laser beamshaving different wavelengths from each other, an optical system forprocessing the plurality of sectional laser beams having differentwavelengths from each other into a linear laser beam in the irradiatedsurface, respectively, and making an energy distribution uniform, and ameans of relatively moving the object to be irradiated to the laserbeam.

In any of the above-mentioned inventions, since the laser oscillator isa YAG laser and the maintenance of the laser apparatus is easy tomanage, productivity is increased and is thus preferable. Further, theYAG laser is capable of generating harmonics readily, and hence issuitable for use in the present invention.

Also, in any of the above-mentioned inventions when the object to beirradiated is a non-single crystal silicon film, laser beams having awavelength of 600 nm or less may be used as the laser beams havingdifferent wavelengths from each other because the processing efficiencyis high. For example, it is good to use the combination the secondharmonic and the third harmonic of the YAG laser, or the combination thesecond harmonic and the fourth harmonic of the YAG laser, or thecombination the third harmonic and the fourth harmonic of the YAG laserbecause the processing efficiency is high. Other than the YAG laser, aYVO4 laser, a glass laser, etc. can be used in the present invention.

Both of the above-mentioned laser apparatuses have a load/unloadchamber, a transfer chamber, a pre-heat chamber, a laser irradiationchamber, and a cooling chamber. Both laser apparatuses are preferred forthey can be used in mass production.

Further, according to another aspect of the present invention, there isprovided a laser irradiation method that simultaneously irradiates eachof a plurality of laser beams having different wavelengths from eachother to a same region, characterized in that the shape of the laserbeam in the same region is square-like or rectangular.

Further, according to another aspect of the present invention, there isprovided a laser irradiation method that simultaneously irradiates eachof a plurality of laser beams having different wavelengths from eachother to a same region, characterized in that the shape of the laserbeam in the same region is linear.

Further, according to another aspect of the present invention, there isprovided a laser irradiation method that simultaneously irradiates eachof a plurality of laser beams having different wavelengths from eachother to a same region of a substrate having a non-single crystalsemiconductor film formed thereon, characterized in that the shape ofthe laser beam in the same region is square-like or rectangular.

Further, according to another aspect of the present invention, there isprovided a laser irradiation method that simultaneously irradiates eachof a plurality of laser beams having different wavelengths from eachother to a same region of a substrate having a non-single crystalsemiconductor film formed thereon, characterized in that the shape ofthe laser beam in the same-region is linear and that the linear laserbeam is irradiated to the non-single crystal semiconductor film whilerelatively scanning the linear laser beam to the non-single crystalsemiconductor film.

Still further, according to another aspect of the present invention,there is provided a method of manufacturing a semiconductor deviceprovided with a TFT formed on a substrate, characterized by comprisingthe steps of forming a non-single crystal semiconductor film on thesubstrate and simultaneously irradiating a plurality of laser beamshaving different wavelengths from each other to a certain region of thenon-single crystal semiconductor film.

Still further, according to another aspect of the present invention,there is provided a method of manufacturing a semiconductor deviceprovided with a TFT formed on a substrate, characterized by comprisingthe steps of forming a non-single crystal semiconductor film on thesubstrate and simultaneously irradiating a plurality of laser beamshaving different wavelengths from each other to a region of thenon-single crystal semiconductor film to thereby transform thenon-single crystal semiconductor film into a crystalline semiconductorfilm.

In any one of the above-mentioned inventions, the laser beam is a YAGlaser and the maintenance of the laser apparatus can be easily managed,and therefore the inventions thereof are appreciated. Also, because theplurality of laser beams having different wavelengths from each otherhave a wavelength of 600 nm or less in any one of the above-mentionedinventions, their absorption to the semiconductor film is large andhence the inventions thereof are appreciated. As laser beams having awavelength of 600 nm or less, there are, for example, the secondharmonic, the third harmonic, and the fourth harmonic of the YAG laser.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome more apparent from the following description taken in conjunctionwith the accompanying drawings:

FIGS. 1A and 1B are diagrams showing a side view and a top view,respectively, of a conventional optical system that forms a linear laserbeam;

FIG. 2 is a view illustrating the structure of a YAG laser of a zigzagslab system;

FIG. 3A is a view showing an energy distribution of a linear laser beamand FIG. 3B is a view showing the state of a silicon film irradiatedwith a linear laser beam while the linear laser beam is scanned in adirection at a right angle in the longitudinal direction thereof;

FIG. 4A is a view showing an example of an optical system processing asecond harmonic of a YAG laser into a linear laser beam by using a beamhomogenizer, and FIG. 4B is a view illustrating a profile of aninterference caused by the second harmonic of the YAG laser which isprocessed into a linear laser beam by using the beam homogenizer;

FIG. 5A is a view showing an example of an optical system using a beamhomogenizer to synthesize a second harmonic and a third harmonic of aYAG laser to thereby form a linear laser beam, and FIG. 5B is viewillustrating a profile of an interference caused by the second harmonicand the third harmonic of the YAG laser which are synthesized andprocessed into a linear laser beam by using the beam homogenizer;

FIG. 6 is a view illustrating a calculation result of an energyintensity distribution of a light interference;

FIG. 7 is a view illustrating a calculation result of an energyintensity distribution of a light interference;

FIG. 8 is a view illustrating a calculation result of an energyintensity distribution of a light interference;

FIG. 9 is a view illustrating a calculation result of an energyintensity distribution of a light interference;

FIG. 10 is a diagram showing an example of a laser irradiation apparatusdisclosed in the present invention;

FIG. 11 is a diagram showing an example of a laser irradiation apparatusdisclosed in the present invention;

FIGS. 12A and 12B are views illustrating a calculation result of anenergy intensity distribution of a light interference;

FIG. 13 is a diagram showing an example of a laser irradiation apparatusdisclosed in the present invention;

FIG. 14 is a diagram showing a laser irradiation apparatus for massproduction;

FIGS. 15A to 15D are diagrams showing an example of a manufacturingprocess of the present invention;

FIGS. 16A to 16D are diagrams showing an example of a manufacturingprocess of the present invention;

FIGS. 17A to 17D are diagrams showing an example of a manufacturingprocess of the present invention;

FIGS. 18A to 18C are diagrams showing an example of a manufacturingprocess of the present invention;

FIG. 19 is a diagram showing an example of a manufacturing process ofthe present invention;

FIG. 20 is a diagram showing a top view of a pixel;

FIG. 21 is a diagram showing the cross-sectional structure of a liquidcrystal display device;

FIGS. 22A to 22C are diagrams showing an example of a manufacturingprocess of the present invention;

FIGS. 23A to 23D are diagrams showing an example of a manufacturingprocess of the present invention;

FIG. 24 is a diagram showing the outer appearance of an AM-LCD;

FIGS. 25A and 25B are diagrams showing the structure of an active matrixtype EL display device;

FIGS. 26A and 26B are diagrams showing the structure of an active matrixtype EL display device;

FIG. 27 is a diagram showing the structure of an active matrix type ELdisplay device;

FIGS. 28A and 28B are diagrams showing the structure of an active matrixtype EL display device;

FIG. 29 is a diagram showing the structure of an active matrix type ELdisplay device;

FIGS. 30A to 30C are diagrams showing a circuit configuration of anactive matrix type EL display device;

FIGS. 31A to 31F are diagrams showing examples of an electronic device;

FIGS. 32A to 32D are diagrams showing examples of an electronic device;

FIGS. 33A to 33C are diagrams showing examples of an electronic device;and

FIG. 34 is a graph illustrating a wavelength dependence of a ratio ofthe absorption of light to a 55 nm-thick a-Si film formed on a glasssubstrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode of the PresentInvention

First, an example of irradiating a laser beam, which has been processedinto a linear laser beam at an irradiated surface, to a 5 inch squaresubstrate having an a-Si film formed thereon as an object to beirradiates is shown.

A 0.7-thick Corning 1737 is used as the substrate. If the Corning 1737substrate has sufficient durability up to a temperature of 600° C. AnSiO₂ film is formed to a thickness of 200 nm on one side of thesubstrate by plasma CVD. Further, a 55 nm-thick a-Si film is formedthereon. As the film deposition method, for example, sputtering or thelike may be used.

The substrate, completed with the formation of the silicon films, isexposed in a nitrogen atmosphere at a temperature of 500° C. for 1 hourto thereby reduce the hydrogen concentration in the a-Si film. The laserresistance of the a-Si film can thus be enhanced. An appropriateconcentration of hydrogen inside the a-Si film is on the order of 10²⁰atoms/cm³. The formation of the object to be irradiated is thuscompleted. Then laser is irradiated to the object to thereby performcrystallization of the a-Si film.

Before performing laser irradiation to the a-Si film, heat may beapplied thereto to perform crystallization. For example, the a-Si filmmay be crystallized by adding therein an element that promotescrystallization and then performing heat treatment. The detailsregarding the method of crystallizing the a-Si film by adding therein anelement that promotes crystallization and then applying heat isexplained in Embodiment 1.

FIG. 13 is a view illustrating a laser irradiation apparatus. The laserirradiation apparatus shown in FIG. 13 is one example of an apparatusthat irradiates a linear laser beam to a substrate. The structurethereof is the same as the optical system shown in FIG. 1. A laser beamis processed into a 115 mm long and 0.5 mm wide linear laser beam by theoptical system shown in FIG. 13. Because the length of the linear laserbeam is 115 mm, it is scanned in one direction to the 5 inch square(about 125 mm) substrate, whereby almost the entire surface of thesubstrate can be irradiated with the laser beam. The optical systemillustrated in FIG. 13 is one example thereof. The linear laser beam isimaged on the a-Si film. The size of the above-mentioned linear laserbeam is the size of the beam when imaged on the a-Si film. The structureof the optical system is explained in the following. A pulse oscillationtype YAG laser oscillator 1301 oscillates a laser beam having afundamental wave (wavelength of 1065 nm), a second harmonic (wavelengthof 533 nm), and a third harmonic (wavelength of 355 nm). Theabove-mentioned YAG laser is a zigzag slab system YAG laser. The sizesof the above laser beams at the exit of the respective laser beams are6×12 mm and rectangular in shape. Further, the largest outputs of thelaser beams are 800 mJ/pulse at the second harmonic and 400 mJ/pulse atthe third harmonic. A largest repetitive frequency is 30 Hz and a pulsewidth is 10 ns.

From the fact that the 533 nm laser beam and the 355 nm laser beamhaving different wavelengths from each other are used, a syntheticquartz that has a high transmittance at the wavelength region thereof isused as the core of the lenses. Because laser beams having differentwavelengths from each other are passed through the optical system, theradius of curvature of the lenses that the second harmonic penetratesand the radius of the curvature of the lenses that the third harmonicpenetrates must be changed even if, for example, the focal lengthsthereof are equivalent. Further, a coating that is appropriate for eachof the wavelengths may be applied to the lenses in order to prevent thesurfaces of the lenses from reflecting and to enhance the transmittance.In addition, the life of the lenses can be extended by applying acoating. Depending on the layout of the laser irradiation apparatus, itis necessary to arrange mirrors in appropriate positions. Progress isbeing made in a technique for making mirrors to have a high reflectanceto a very wide range of wavelengths. There are mirrors in which nearly99% or more reflectance can be obtained from both the 355 nm wavelengthand the 533 nm wavelength. Of course, different coatings may be used inaccordance with different wavelengths because a higher reflectance canbe obtained.

The fundamental wave generated from a resonator 1302 of the YAG laser isconverted into the second harmonic and the third harmonic by anon-linear optical element 1303. Because components of the fundamentalwave still remain in the laser beam, the components thereof areseparated from that of the second harmonic and the third harmonic by abeam splitter 1304 that is arranged at a 45 degree angle to theadvancing direction of the laser beam. The laser beam that istransmitted from the beam splitter 1304 is the fundamental wave and thelaser beam that is reflected is the second harmonic and the thirdharmonic.

The second harmonic and the third harmonic are separated by a beamsplitter 1305 that is arranged at a 45 degree angle to the advancingdirection of the second harmonic and the third harmonic. The laser beamthat is reflected by the beam splitter 1305 is the second harmonic andthe laser beam that transmitted thereby is the third harmonic. Next, thelight path of the third harmonic is bend 90 degrees upward by a mirror1306 and then further bend 90 degrees in a horizontal direction by amirror 1307. Thus, the advancing direction of the third harmonic isconverted into a direction that is the same as the advancing directionof the second harmonic. At this point, the fundamental wave, the secondharmonic, and the third harmonic are simultaneously outputted at theexit of the laser beam, respectively. A positional relationship of thelaser beams of the second harmonic and the third harmonic is set so thatthe diagonal line of the rectangular laser beam is on top of the samelinear line.

The second harmonic separated by the beam splitter 1305 is once splitinto 2 beams by a cylindrical lens array 13082. Thereafter, the splitbeam is converged into 1 beam at an irradiated surface 1313 by acylindrical lens 13102 and a cylindrical lens 13121. The cylindricallens 13102 and the cylindrical lens 13121 have the shape of acylindrical lens after it has been separated into 2 congruent solidcylindrical lenses at a plane containing a straight line that is calledthe main line (mother line) of a normal cylindrical lens. Such lensesare called half cylindrical lenses throughout the present specification.

The second harmonic that has been split into 4 beams by a cylindricallens array 13092 is converged into 1 beam at the irradiated surface 1313by a cylindrical lens 13111.

A coating is applied on the cylindrical lens array 13082, thecylindrical lens array 13092, the cylindrical lens 13102, thecylindrical lens 13111, and the cylindrical lens 13121, respectively, inorder to make the transmittance of the 533 nm wavelength second harmonicto 99% or more.

On the other hand, the third harmonic reflected by the mirror 1307 isonce split into 2 beams by a cylindrical lens array 13081. Thereafter,the split beam is converged into 1 beam at the irradiated surface 1313by a cylindrical lens 13101 and a cylindrical lens 13122. Thecylindrical lens 13101 and the cylindrical lens 13122 are halfcylindrical lenses.

The third harmonic that has been further split into 4 beams by acylindrical lens array 13091 is converged into 1 beam at the irradiatedsurface 1313 by a cylindrical lens 13112.

A coating is applied on the cylindrical lens array 13081, thecylindrical lens array 13091, the cylindrical lens 13101, thecylindrical lens 13112, and the cylindrical lens 13122, respectively, inorder to make the transmittance of the 355 nm wavelength third harmonicto 99% or more.

Examples of specific sizes and focal lengths of the optical systemillustrated in FIG. 13 are shown here in the following. The lenses shownherein below are all cylindrical lenses and have a radius of curvaturein the width direction.

First, the structure of the optical system which processes the secondharmonic is described. The cylindrical lens array 13082 is made up of 2cylindrical lenses that are 3 mm wide, 25 mm long, 3 mm thick with afocal length of 300 mm and combined with each other in the widthdirection in the form of an array.

The above-mentioned cylindrical lens is a planoconvex lens having aspherical convex surface. Throughout the present specification, theincident surfaces of the lenses are spherical and the other surfaces areplanar unless particularly stated. To make the lenses into an arrayform, a method that may be used is by adhering them together by applyingheat or fitting the lenses into a frame and then fixing them from theoutside. In addition, the cylindrical lens arrays may be formed into oneunit of cylindrical lens array at the grinding stage.

The cylindrical lens array 13092 is made up of 4 cylindrical lenses thatare 3 mm wide, 30 mm long, 3 mm thick with a focal length of 25 mm, andcombined with each other in the width direction in the form of an array.

The cylindrical lens 13102 is a half cylindrical lens that is 30 mmwide, 80 mm long, 8 mm thick, and has a focal length of 300 mm.

The cylindrical lens 13111 is a cylindrical lens that is 150 mm wide, 40mm long, 15 mm thick, and has a focal length of 1000 mm.

The cylindrical lens 13121 is a half cylindrical lens that is 40 mmwide, 150 mm long, and 15 mm thick with a focal length of 175 mm. Inorder to enhance the uniformity of the linear laser beam at theirradiated surface 1313, it is better that the cylindrical lens 13121 isa non-spherical lens. If non-spherical lenses are hard to process, thenit is better to use a set lens such as, for example, a doublet lens or atriplet lens to thereby suppress the spherical aberrations.

Next, the structure of the optical system which processes the thirdharmonic is described. The cylindrical lens array 13081 is made up of 2cylindrical lenses that are 3 mm wide, 25 mm long, 3 mm thick with afocal length of 300 mm and combined with each other in the widthdirection in the form of an array.

The cylindrical lens array 13091 is made up of 4 cylindrical lenses thatare 3 mm wide, 30 mm long, 3 mm thick with a focal length of 25 mm, andcombined with each other in the width direction in the form of an array.

The cylindrical lens 13101 is a half cylindrical lens that is 30 mmwide, 80 mm long, 8 mm thick, and has a focal length of 300 mm,

The cylindrical lens 13112 is a cylindrical lens that is 150 mm wide, 40mm long, 15 mm thick, and has a focal length of 1000 mm.

The cylindrical lens 13122 is a half cylindrical lens that is 40 mmwide, 150 mm long, and 15 mm thick with a focal length of 175 mm. Inorder to enhance the uniformity of the linear laser beam at theirradiated surface 1313, it is better that the cylindrical lens 13122 isa non-spherical lens. If non-spherical lenses are hard to process, thenit is better to use a set lens such as, for example, a doublet lens or atriplet lens to thereby suppress the spherical aberrations.

Note that for the purpose of protecting the optical system, theatmosphere around the optical system may contain a gas, such asnitrogen, that does not easily react to the lens coating substance.Therefore, the optical system may be enclosed in an optical systemprotection chamber. Using quartz, which has been applied with a coatingin accordance to the respective wavelengths, for a window where a laserenters and exits the optical system protection chamber is good because ahigh transmittance of 99% or more can thus be obtained.

The substrate having the a-Si film formed thereon is placed on theirradiated surface 1313 where a stage (not shown), is moved at aconstant speed by using a moving mechanism (not shown), in thelongitudinal direction and the right angle direction of the linear laserbeam (the direction indicated by an arrow) while irradiating the laserbeam. Thus, the laser beam can be irradiated on the entire surface ofthe substrate. A ball screw type, a linear motor, or the like can beused as the moving mechanism.

The irradiation conditions may be determined within the range of thefollowing standards.

Energy density of a linear laser beam: 50 to 500 mJ/cm²

Moving speed of the stage: 0.1 to 2 mm/s

Oscillation frequency of a laser oscillator: 30 Hz

The above stated irradiation conditions change in accordance with thepulse width of the laser oscillator, the state of the semiconductorfilm, and the specification of the device to be manufactured. Animplementor will have to determine the details of the conditionsappropriately. Furthermore, the value of the frequency of the laseroscillator is set to a value which is considered to be the highest valueamong the large output YAG lasers sold in the current market. If laserswith a higher frequency are developed in the future, it is suitable toadopt the higher frequency as much as possible in order to improvethroughput. However, if attempts are made to obtain a higher frequencyat the present level, the quality of the laser beam becomes very poor.That is, M² becomes poor, and therefore it is better to use a frequencyof about 30 Hz.

The atmosphere during the irradiation of the laser beam is set to theatmosphere of a clean room. For example, the atmosphere of the cleanroom is air at a temperature of 23° C. As other replacements of theatmosphere, a chamber may be provided and air may be replaced by H₂.Replacements of the atmosphere are performed to prevent contamination ofthe substrate and to prevent the surface of the semiconductor film frombecoming rough. Gas is supplied through a gas cylinder. Theabove-mentioned atmosphere may be H₂, He, N₂, or Ar or a gaseous mixturethereof. In addition, making the atmosphere into a vacuum (10⁻¹ torr orless) also has the contamination prevention effect and the effect ofpreventing the surface from becoming rough.

Besides using the Corning 1737 as the substrate, the Corning 7059 and aglass substrate such as the AN100 can be used, or a quartz substrate maybe used.

During the irradiation of the laser beam, when a spot of the substrateirradiated with the linear laser beam is heated by applying a stronglight using an infrared lamp or the like, the energy of the laser beamcan be reduced compared with the case of not heating the spot of thesubstrate. Heat may also be applied by placing a heater at a bottomportion of the substrate. When the linear laser beam is made longer sothat it may be used for a larger area substrate, the aid of energy dueto the application of heat is useful when the energy of the laser beamis insufficient.

The laser irradiation apparatus of the present invention is applicablenot only to the non-single crystal silicon film, but also to othernon-single crystal semiconductor films such as, for example, anon-single crystal semiconductor film of a diamond or germanium.

Employing the semiconductor film crystallized by the above-mentionedlaser irradiation apparatus, a semiconductor device such as a liquidcrystal display of a low temperature poly-silicon TFT may bemanufactured by a known method, or a semiconductor device contrived byan implementor may be manufactured.

Embodiment 1

In the present embodiment, an example will be described in which apolycrystalline silicon film is irradiated with a laser beam. The laserirradiation device described in the above embodiment mode is used.

A Corning glass 1737 having a thickness of 0.7 mm is used as asubstrate. The substrate has sufficient durability if it is used under600° C. An SiO₂ film is formed in 200 nm on one surface of the substrateby a plasma CVD method. Further, an a-Si film is formed in 55 nm on theSiO₂ film. Any other film forming method, for example, a sputteringmethod may be used.

Next, the above-mentioned a-Si film is crystallized by the methoddisclosed in Japanese Patent Laid-Open No. 7-130652. The method will bedescribed briefly in the following. The above a-Si film is coated with anickel acetate water solution having a concentration of 10 ppm and thenis heated in a nitrogen atmosphere at 550° C. for 4 hours, whereby thea-Si film is crystallized. It is recommended that a spin coat method,for example, be used for applying the nickel acetate water solution. Thea-Si film to which nickel is added is crystallized in a short period atlow temperatures. It is thought that this is because the nickel acts asthe seed crystal of crystal growth to facilitate the crystal growth.

If the polycrystalline silicon film crystallized by the above method isirradiated with the laser beam, it has higher characteristics as amaterial of a semiconductor element. Accordingly, to improve thecharacteristics of the above polycrystalline silicon film, the abovepolycrystalline silicon film is irradiated with the laser beam by usingthe laser irradiation device used in the embodiment mode of the presentinvention.

It is recommended that a semiconductor device, for example, a liquidcrystal display made of low-temperature polysilicon TFTs, ismanufactured by using a semiconductor film crystallized with the abovelaser irradiation device by a publicly known method. Or a semiconductordevice invented by a practicing person can be manufactured. Theembodiment mode of the present invention and the embodiment 1 can beused in combination.

Embodiment 2

Shown in Embodiment 2 is an example of linearly synthesizing the secondharmonic and the fourth harmonic of the YAG laser at the irradiatedsurface as the light source of the laser beam.

The advantages of using the second harmonic are that a large output canbe obtained, and further, the optical lenses do not deteriorate easily.By mixing the fourth harmonic with the second harmonic, the influence ofinterference in the irradiated surface can thus be remarkably reduced.

A method of Embodiment 2 is that a non-linear optical element whichforms the second harmonic and the fourth harmonic at the same time isused instead of the non-linear optical element used in the EmbodimentMode of the present invention. Furthermore, a similar optical system forprocessing the fourth harmonic is used in place of the portion of theoptical system, which processes the third harmonic. The fourth harmonicmay be entered into the optical system.

Embodiment 2 can be combined with Embodiment 1.

Embodiment 3

Shown in Embodiment 3 is an example of linearly synthesizing the thirdharmonic and the fourth harmonic of the YAG laser at the irradiatedsurface as the light source of the laser beam.

The advantage of using the third harmonic and the fourth harmonic isthat both laser beams have an extremely high absorption coefficient withrespect to silicon films. By mixing the fourth harmonic with the thirdharmonic, the influence of interference in the irradiated surface canthus be remarkably reduced.

A method of Embodiment 3 is that a non-linear optical element whichforms the third harmonic and the fourth harmonic at the same time isused instead of the non-linear optical element used in the EmbodimentMode of the present invention. Furthermore, a similar optical system forprocessing the fourth harmonic is used in place of the portion of theoptical system, which processes the second harmonic. The fourth harmonicmay be entered into the optical system.

Embodiment 3 can be combined with Embodiment 1.

Embodiment 4

In the present embodiment, an example of a laser irradiation device formass production will be described with reference to FIG. 14. FIG. 14 isa top view of a laser irradiation device.

A substrate is carried from a load/unload chamber 1401 by the use of acarrying robot arm 1403 mounted in a transfer chamber 1402. First, thesubstrate is aligned in an alignment chamber 1404 and then is carried toa pre-heat chamber 1405. In the pre-heat chamber 1405, the substrate ispreviously heated to a desired temperature of about 300° C., forexample, by the use of an infrared lamp heater. Then, the substrate isplaced in a laser irradiation chamber 1407 via a gate valve 1406 andthen the gate valve 1406 is closed.

A laser beam is emitted by the laser oscillator 1400 described in theembodiment mode and then is bent downward 90 degrees by a mirror (notshown) placed directly above a quartz window 1410 via an optical system1409 and is transformed into a linear laser beam at an irradiate surfacein the laser irradiation chamber 1407 via the quartz window 1410. Thelaser beam is applied to the substrate placed at the irradiate surface.It is recommended that the above-mentioned optical system be used as theoptical system 1409, or the one similar to the optical system may beused. It is preferable to use excimer grade quartz window. The excimergrade quartz window can be used at a state of non-coat, because it hassufficiently transmittance against the second harmonic and the thirdharmonic.

The laser irradiation chamber 1407 is evacuated by a vacuum pump 1411 tomake the atmosphere of the chamber 1407 a high vacuum of about 10⁻3 Pabefore the irradiation of the laser beam, or the atmosphere of the laserirradiation chamber 1407 is made a desired atmosphere by the vacuum pump1411 and a gas cylinder 1412. As described above, the above atmospheremay be He, Ar, H₂, or the mixed gas of them.

Then, the substrate is scanned and irradiated with the linear laser beammoved by a moving mechanism 1413. At this time, an infrared lamp (notshown) may be applied to the spot of the substrate irradiated with thelinear laser beam.

After the end of the irradiation of the laser beam, the substrate iscarried to a cooling chamber 1408 to be allowed to cool slowly and thenis returned to the load/unload chamber 1401 via the alignment chamber1404. In this manner, many substrates can be annealed with laser byrepeating these actions.

The embodiment 4 can be used in combination with the embodiment mode andthe other embodiments of the present invention.

Embodiment 5

The present embodiment is described by using FIGS. 15 to 21. Here, themethod of fabricating pixel TFTs for the display region and TFTs ofdriving circuits provided in the periphery of the display region, over asame substrate, and a display device manufactured by using it will bedescribed in detail in accordance with the fabricating steps. However,in order to simplify the description, CMOS circuits that are the basiccircuits of a shift register circuit, a buffer circuit, and the like forthe control circuit and n-channel type TFTs that form sampling circuitswill be shown in the figures.

In FIG. 15A, a low-alkaline glass substrate or a quartz substrate can beused as a substrate 1501. In this embodiment, a low-alkaline glasssubstrate was used. On the surface of this substrate 1501 on which TFTsare to be formed, a base film 1502 such as a silicon oxide film, asilicon nitride film or a silicon oxynitride film is formed in order toprevent the diffusion of impurities from the substrate 1501. Forexample, a silicon oxynitride film which is fabricated from SiH₄, NH₃,N₂O by plasma CVD into 100 nm and a silicon oxynitride film which issimilarly fabricated from SiH₄ and N₂O into 200 nm are formed into alaminate.

Next, a semiconductor film 1503 a that has an amorphous structure and athickness of 20 to 150 nm (preferably, 30 to 80 nm) is formed by a knownmethod such as plasma CVD or sputtering. In this embodiment, anamorphous silicon film was formed to a thickness of 55 nm by plasma CVD.As semiconductor films which have an amorphous structure, there are anamorphous semiconductor film and a microcrystalline semiconductor film;and a compound semiconductor film with an amorphous structure such as anamorphous silicon germanium film may also be applied. Further, the basefilm 1502 and the amorphous silicon film 1503 a can be formed by thesame deposition method, so that the two films can be formed insuccession. By not exposing the base film to the atmospheric air afterthe formation of the base film, the surface of the base film can beprevented from being contaminated, as a result of which the dispersionin characteristics of the fabricated TFTs and the variation in thethreshold voltage thereof can be reduced. (FIG. 15A)

Then, by a known crystallization technique, a crystalline silicon film1503 b is formed from the amorphous silicon film 1503 a. In the presentembodiment, laser crystallization was performed in accordance with theabove stated embodiment mode by using a laser apparatus of the presentinvention. It is preferred that, prior to the crystallization step, heattreatment is carried out at 400 to 500° C. for about one hour though itdepends on the amount of hydrogen contained, so that, after the amountof hydrogen contained is reduced to 5 atom % or less, thecrystallization is carried out. (FIG. 15B)

Then, the crystalline silicon film 1503 b is divided into islands, toform island semiconductor layers 1504 to 1507. Thereafter, a mask layer1508 of a silicon oxide film is formed to a thickness of 50 to 100 nm byplasma CVD or sputtering. (FIG. 15C)

Then, a resist mask 1509 is provided, and, into the whole surfaces ofthe island semiconductor layers 1505 to 1507 forming the n-channel typeTFTs, boron (B) was added as an impurity element imparting p-typeconductivity, at a concentration of about 1×10¹⁶ to 5×10¹⁷ atoms/cm³,for the purpose of controlling the threshold voltage. The addition ofboron (B) may be performed either by the ion doping or it may be addedsimultaneously when the amorphous silicon film is formed. The additionof boron (B) here was not always necessary, however, the formation ofsemiconductor layers 1510 to 1512 into which boron was added waspreferable for maintaining the threshold voltage of the n-channel typeTFTs within a prescribed range. (FIG. 15D)

In order to form the LDD regions of the n-channel type TFTs in thedriving circuit, an impurity element imparting n-type conductivity isselectively added to the island semiconductor layers 1510 and 1511. Forthis purpose, resist masks 1513 to 1516 were formed in advance. As theimpurity element imparting the n-type conductivity, phosphorus (P) orarsenic (As) may be used; here, in order to add phosphorus (P), iondoping using phosphine (PH₃) was applied. The concentration ofphosphorus (P) in the impurity regions 1517 and 1518 thus formed may beset within the range of from 2×10¹⁶ to 5×10¹⁹ atoms/cm³. In thisspecification, the concentration of the impurity element contained inthe thus formed impurity regions 1517 to 1519 imparting n-typeconductivity is represented by (n⁻). Further, the impurity region 1519is a semiconductor layer for forming the storage capacitor of the pixelmatrix circuit; into this region, phosphorus (P) was also added at thesame concentration. (FIG. 16A)

Next, the mask layer 1508 is removed by hydrofluoric acid or the like,and the step of activating the impurity elements added at the stepsshown in FIG. 15D and FIG. 16A is carried out. The activation can becarried out by performing heat treatment in a nitrogen atmosphere at 500to 600° C. for 1 to 4 hours or by using the laser activation method.Further, both methods may be jointly performed. Or, the laserirradiation described in the embodiment mode may be performed. In thisembodiment, the laser activation method was employed, and a KrF excimerlaser beam (with a wavelength of 248 nm) was used; the beam is formedinto a linear beam; and scan was carried out under the condition thatthe oscillation frequency was 5 to 50 Hz, the energy density was 100 to500 mJ/cm², and the overlap ratio of the linear beam was 80 to 98%,whereby the whole substrate surface on which the island semiconductorlayers were formed was processed. Any item of the laser irradiationcondition is subjected to no limitation, so that the operator maysuitably select the condition.

Then, a gate insulating film 1520 is formed of an insulating filmcomprising silicon to a thickness of 10 to 150 nm, by plasma CVD orsputtering. For example, a silicon oxynitride film is formed to athickness of 120 nm. As the gate insulating film, other insulating filmscomprising silicon may be used as a single layer or a laminatestructure. (FIG. 16B)

Next, in order to form a gate electrode, a first conductive layer isdeposited. This first conductive layer may be formed of a single layerbut may also be formed of a laminate consisting of two or three layers.In this embodiment, a conductive layer (A) 1521 comprising a conductivemetal nitride film and a conductive layer (B) 1522 comprising a metalfilm are laminated. The conductive layer (B) 1522 may be formed of anelement selected from among tantalum (Ta), titanium (Ti), molybdenum(Mo) and tungsten (W) or an alloy comprised mainly of theabove-mentioned element, or an alloy film (typically, an Mo—W alloy filmor an Mo—Ta alloy film) comprised of a combination of theabove-mentioned elements, while the conductive layer (A) 1521 is formedof a tantalum nitride (TaN) film, a tungsten nitride (WN) film, atitanium nitride (TiN) film, or a molybdenum nitride (MoN) film.Further, as the substitute materials of the conductive film (A) 1521,tungsten silicide, titanium silicide, and molybdenum silicide may alsobe applied. The conductive layer (B) may preferably have its impurityconcentration reduced in order to decrease the resistance thereof; inparticular, as for the oxygen concentration, the concentration may beset to 30 ppm or less. For example, tungsten (W) could result inrealizing a resistivity of 20 μΩcm or less by rendering the oxygenconcentration thereof to 30 ppm or less.

The conductive layer (A) 1521 may be set to 10 to 50 nm (preferably, 20to 30 nm), and the conductive layer (B) 1522 may be set to 200 to 400 nm(preferably, 250 to 350 nm). In this embodiment, as the conductive layer(A) 1521, a tantalum nitride film with a thickness of 30 nm was used,while, as the conductive layer (B) 1522, a Ta film with a thickness of350 nm was used, both films being formed by sputtering. In case ofperforming sputtering here, if a suitable amount of Xe or Kr is addedinto the sputtering gas Ar, the internal stress of the film formed isalleviated, whereby the film can be prevented from peeling off. Thoughnot shown, it is effective to form a silicon film, into which phosphorus(P) is doped, to a thickness of about 2 to 20 nm underneath theconductive layer (A) 1521. By doing so, the adhesiveness of theconductive film formed thereon can be enhanced, and at the same time,oxidation can be prevented. In addition, the alkali metal elementslightly contained in the conductive layer (A) or the conductive layer(B) can be prevented from diffusing into the gate insulating film 1520.(FIG. 16C)

Next, resist masks 1523 to 1527 are formed, and the conductive layer (A)1521 and the conductive layer (B) 1522 are etched together to form gateelectrodes 1528 to 1531 and a capacitor wiring 1532. The gate electrodes1528 to 1531 and the capacitor wiring 1532 are formed in such a mannerthat the layers 1528 a to 1532 a comprised of the conductive layer (A)and the layers 1528 b to 1532 b comprised of the conductive layer (B)are respectively formed integrally. In this case, the gate electrodes1529 and 1530 formed in the driving circuit are formed so as to overlapthe portions of the impurity regions 1517 and 1518 through the gateinsulating film 1520. (FIG. 16D) Then, in order to form the sourceregion and the drain region of the p-channel TFT in the driving circuit,the step of adding an impurity element imparting p-type conductivity iscarried out. Here, by using the gate electrode 1528 as a mask, impurityregions are formed in a self-alignment manner. In this case, the regionin which the n-channel TFT will be formed is coated with a resist mask1533 in advance. Thus, impurity regions 1534 were formed by ion dopingusing diborane (B₂H₆). The concentration of boron (B) in this region isset at 3×10²⁰ to 3×10²¹ atoms/cm³. In this specification, theconcentration of the impurity element imparting p-type contained in theimpurity regions 1534 is represented by (p⁺). (FIG. 17A)

Next, in the n-channel TFTs, impurity regions that function as sourceregions or drain regions were formed. Resist masks 1535 to 1537 wereformed, and impurity regions 1538 to 1542 were formed by adding animpurity element for imparting the n-type conductivity. This was carriedout by ion doping using phosphine (PH₃), and the phosphorus (P)concentration in these regions was set to 1×10²⁰ to 1×10²¹ atoms/cm³. Inthis specification, the concentration of the impurity element impartingthe n-type contained in the impurity regions 1538 to 1542 formed here isrepresented by (n⁺). (FIG. 17B)

In the impurity regions 1538 to 1542, the phosphorus (P) or boron (B)which was added at the preceding steps are contained, however, ascompared with this impurity element concentration, phosphorus is addedhere at a sufficiently high concentration, so that the influence by thephosphorus (P) or boron (B) added at the preceding steps need not betaken into consideration. Further, the concentration of the phosphorus(P) that is added into the impurity regions 1538 is ½ to ⅓ of theconcentration of the boron (B) added at the step shown in FIG. 17A; andthus, the p-type conductivity was guaranteed, and no influence wasexerted on the characteristics of the TFTs.

Then, the step of adding an impurity imparting n-type is performed toform the LDD regions of the n-channel type TFTs in the pixel matrixcircuit. Here, by using the gate electrode 1531 as a mask, the impurityelement for imparting n-type was added in a self-alignment manner. Theconcentration of phosphorus (P) added was 1×10¹⁶ to 5×10¹⁸ atoms/cm³; bythus adding phosphorus at a concentration lower than the concentrationsof the impurity elements added at the steps shown in FIG. 16A, FIG. 17Aand FIG. 17B, only impurity regions 1543 and 1544 were substantiallyformed. In this specification, the concentration of the impurity elementfor imparting the n-type conductivity contained in these impurityregions 1543 and 1544 is represented by (n⁻⁻). (FIG. 17C)

Thereafter, in order to activate the impurity elements, which were addedat their respective concentrations for imparting n-type or p-typeconductivity, a heat treatment step was carried out. This step can becarried out by furnace annealing, laser annealing or rapid thermalannealing (RTA). Here, the activation step was performed by furnaceannealing. Heat treatment is carried out in a nitrogen atmosphere withan oxygen concentration of 1 ppm or less, preferably 0.1 ppm or less, at400 to 800° C., typically at 500 to 600° C.; in this embodiment, theheat treatment was carried out at 550° C. for 4 hours. Further, in thecase a substrate such as a quartz substrate which has heat resistance isused as the substrate 1501, the heat treatment may be carried out at800° C. for one hour; in this case, the activation of the impurityelements and the junctions between the impurity regions into which theimpurity element was added and the channel forming region could be wellformed.

By this heat treatment, on the metal films 1528 b to 1532 b, which formthe gate electrodes 1528 to 1531 and the capacitor wiring 1532,conductive layers (C) 1528 c to 1532 c are formed with a thickness of 5to 80 nm as measured from the surface. For example, in the case theconductive layers (B) 1528 b to 1532 b are made of tungsten (W),tungsten nitride (WN) is formed; in the case of tantalum (Ta), tantalumnitride (TaN) can be formed. Further, the conductive layers (C) 1528 cto 1532 c can be similarly formed by exposing the gate electrodes 1528to 1531 to a plasma atmosphere containing nitrogen using nitrogen,ammonia or the like. Further, heat treatment was carried out in anatmosphere containing 3 to 100% of hydrogen at 300 to 450° C. for 1 to12 hours, thus performing the step of hydrogenating the islandsemiconductor layers. This step is a step for terminating the danglingbonds of the semiconductor layers by the thermally excited hydrogen. Asanother means for the hydrogenation, plasma hydrogenation (using thehydrogen excited by plasma) may be performed. (FIG. 17D)

After the activation and hydrogenation steps are over, a secondconductive film is formed as gate wiring. This second conductive film ispreferably formed of a conductive layer (D) comprised mainly of aluminum(Al) or copper (Cu) that is a low resistance material, and a conductivelayer (E) comprised of titanium (Ti), tantalum (Ta), tungsten (W), ormolybdenum (Mo). In this embodiment, the second conductive film wasformed by using, as the conductive layer (D) 1545, an aluminum (Al) filmcontaining 0.1 to 2 wt % of titanium (Ti), and by using a titanium (Ti)film as the conductive layer (E) 1546. The conductive layer (D) 1545 maybe formed to a thickness of 200 to 400 nm (preferably, 250 to 350 nm),while the conductive layer (E) 1546 may be formed to a thickness of 50to 200 nm (preferably, 100 to 150 nm). (FIG. 18A)

Then, in order to form gate wirings connected to the gate electrodes,the conductive layer (E) 1546 and the conductive layer (D) 1545 wereetched, whereby gate wirings 1547, 1548 and a capacitor wiring 1549 wereformed. The etching treatment was carried out in such a manner that, atfirst, by a dry etching method using a mixture gas of SiCl₄, Cl₂ andBCl₃, the portions extending from the surface of the conductive layer(E) to a part of the way of the conductive layer (D) were removed, and,thereafter, the conductive layer (D) was removed by wet etching using aphosphoric acid etching solution, whereby the gate wirings could beformed, maintaining a selective workability with respect to the basefilm.(FIG. 18B)

A first interlayer insulating film 1550 is formed of a silicon oxidefilm or a silicon oxynitride film with a thickness of 500 to 1500 nm,and contact holes reaching the source regions or the drain regions,which are formed in the respective island semiconductor layers, areformed; and source wirings 1551 to 1554 and drain wirings 1555 to 1558are formed. Though not shown, in this embodiment, these electrodes wereformed from a laminate film of three-layer structure which was formed bysuccessively forming by sputtering: a Ti film to 100 nm; an aluminumfilm containing Ti to 300 nm; and a Ti film to 150 nm.

Next, as a passivation film 1559, a silicon nitride film, a siliconoxide film or a silicon oxynitride film is formed to a thickness of 50to 500 nm (typically 100 to 300 nm). In the case that a hydrogenatingtreatment was carried out in this state, a preferable result wasobtained in respect of the enhancement in characteristics of the TFTs.For example, it is preferable to carry out heat treatment in anatmosphere containing 3 to 100% of hydrogen at 300 to 450° C. for 1 to12 hours; or, in the case that the plasma hydrogenation method wasemployed, a similar effect was obtained. Here, openings may be formed inthe passivation film 1559 at the positions at which contact holes forconnecting the pixel electrodes and drain wirings to each other will beformed later. (FIG. 18C)

Thereafter, a second interlayer insulating film 1560 comprised of anorganic resin is formed to a thickness of 1.0 to 1.5 μm. As the organicresin, polyimide, acrylic, polyamide, polyimideamide, or BCB(benzocyclobutene) can be used. Here, the second interlayer film wasformed by using a polyimide of the type which thermally polymerizesafter applied to the substrate, and it was fired at 300° C. Then, acontact hole reaching the drain wiring 1558 was formed in the secondinterlayer insulating film 1560, and pixel electrodes 1561 and 1562 wereformed. The pixel electrodes may use a transparent conductive film inthe case a transmission type liquid crystal display device is to beobtained, while, in the case a reflection type liquid crystal displaydevice is to be fabricated, it may use a metal film. In this embodiment,a transmission type liquid crystal display device is to be fabricated,so that an indium tin oxide (ITO) film was formed to a thickness of 100nm by sputtering. (FIG. 19)

In this way, a substrate having the TFTs of the driving circuit and thepixel TFTs of the display region on the same substrate could becompleted. In the driving circuit, there were formed a p-channel TFT1601, a first n-channel TFT 1602 and a second n-channel TFT 1603, while,in the display region, there were formed a pixel TFT 1604 and a storagecapacitor 1605. In this specification, such a substrate is called activematrix substrate for convenience.

Note that FIG. 20 is a top view showing almost one pixel in the displayregion. The cross section along with A-A′ shown in FIG. 20 correspondsto the cross sectional diagram of the display region shown in FIG. 19.Further, common reference numerals are used in FIG. 20 to correspondwith the cross sectional diagrams of FIGS. 15 to 19. The gate wiring1548 intersects, by interposing a gate insulating film that is not shownin the figure, with a semiconductor layer 1507 underneath. Though notshown, a source region, a drain region, and a Loff region which isformed from n⁻⁻ region are formed in the semiconductor layer. Referencenumeral 1563 denotes a contact section of the source wiring 1554 and thesource region 1624; 1564, a contact section of the drain wiring 1558 andthe drain region 1626; 1565, a contact section of the drain wiring 1558and the pixel electrode 1561. Storage capacitor 1605 is formed in theregion where a semiconductor layer 1627 extended from the drain region1626 of the pixel TFT 1604 overlap capacitor wirings 1532 and 1549 byinterposing a gate insulating film.

The p-channel TFT 1601 in the driving circuit has a channel formingregion 1606, source regions 1607 a and 1607 b and drain regions 1608 aand 1608 b in the island semiconductor layer 1504. The first n-channelTFT 1602 has a channel forming region 1609, a LDD region 1610overlapping the gate electrode 1529 (such a LDD region will hereinafterbe referred to as Lov), a source region 1611 and a drain region 1612 inthe island semiconductor layer 1505. The length in the channel directionof this Lov region is set to 0.5 to 3.0 μm, preferably 1.0 to 1.5 μm. Asecond n-channel TFT 1603 has a channel forming region 1613, LDD regions1614 and 1615, a source region 1616 and a drain region 1617 in theisland semiconductor layer 1506. In these LDD regions, there are formedan Lov region and a LDD region which does not overlap the gate electrode1530 (such an LDD region will hereafter be referred as Loff); and thelength in the channel direction of this Loff region is 0.3 to 2.0 μm,preferably 0.5 to 1.5 μm. The pixel TFT 1604 has channel forming regions1618 and 1619, Loff regions 1620 to 1623, and source or drain regions1624 to 1626 in the island semiconductor layer 1507. The length in thechannel direction of the Loff regions is 0.5 to 3.0 μm, preferably 1.5to 2.5 μm. Further, the storage capacitor 1605 comprises capacitorwirings 1532 and 1549, an insulating film composed of the same materialas the gate insulating film, and a semiconductor layer 1627 which isconnected to the drain region 1626 of the pixel TFT 1604 and in which animpurity element for imparting the n-type conductivity is added. It isnot necessary to limit the present invention to the structure of thestorage capacitor shown in the present embodiment. For example, storagecapacitors of the structures disclosed in Japanese Patent ApplicationNo. Hei 9-316567, Hei 9-273444 or 10-254097, of the present applicant,can be used.

In FIG. 19, the pixel TFT 1604 is of the double gate structure, but maybe of the single gate structure, or may be of a multi-gate structure inwhich a plurality of gate electrodes are provided.

The processes for manufacturing an active matrix liquid crystal displaydevice from the above stated active matrix substrate is described. Asshown in FIG. 21, an alignment film 1701 is formed onto the activematrix substrate of the state of FIG. 19 manufactured through the abovestated method. Polyimide resin is used in general for an alignment filmof a liquid crystal display element. A shielding film 1703, atransparent conductive film 1704 and an alignment film 1705 are formedon the opposing substrate 1702 on the opposite side. After forming thealignment film, rubbing treatment is performed to make the liquidcrystal molecules orient with a constant pre-tilt angle. The activematrix substrate formed with the pixel matrix circuit and the CMOScircuits, and the opposing substrate are stuck together by a sealant(not shown) or column spacers 1707 through a known cell assemblyprocess. Liquid crystal material 1706 is then injected between thesubstrates and completely sealed by a sealant (not shown). Known liquidcrystal materials can be used for the liquid crystal materials. Anactive matrix liquid crystal display device shown in FIG. 21 is thuscomplete.

As described above, an active matrix liquid crystal display device inwhich TFT structures that comprise each circuit are optimized inaccordance with the specification required by the pixel TFT and thedriver circuit, can be formed.

Note that any constitution of the Embodiments 1 to 12 may be used inmanufacturing a semiconductor device shown in the present embodiment,and it is possible to freely combine each embodiments.

Embodiment 6

Referring to FIGS. 22A to 22C, an example of using another method ofcrystallization, substituting the crystallization step in Embodiment 5,is shown here in Embodiment 6.

First, the state of FIG. 22A is obtained in accordance with Embodiment5. Note that FIG. 22A corresponds to FIG. 15A.

A catalyst element for promoting crystallization (one or plural kinds ofelements selected from a group consisting of nickel, cobalt, germanium,tin, lead, palladium, iron, and copper, typically nickel) is used forperforming crystallization. Specifically, laser crystallization isperformed under a state in which the catalyst element is maintained in asurface of an amorphous silicon film to transform the amorphous siliconfilm into a crystalline silicon film. In Embodiment 6, an aqueoussolution containing nickel (aqueous nickel acetate solution) is appliedto the amorphous silicon film by spin coating to form acatalyst-element-containing layer 1801 on the entire surface of anamorphous semiconductor film 1503 a. (FIG. 22B) The spin coating methodis employed as a means of doping nickel in Embodiment 6. However, othermethods such as evaporation and sputtering may be used for forming athin film containing a metal element (nickel film in the case ofEmbodiment 6) on the amorphous semiconductor film.

Employing the method of irradiating a laser stated in the embodimentmode of the present invention, a crystalline silicon film 1802 is formednext. (FIG. 22C)

By performing the rest of the process in accordance with the steps afterFIG. 15C indicated in Embodiment 5, the structure shown in FIG. 21 canbe attained

If an island-like semiconductor layer is manufactured from the amorphoussilicon film crystallized by using a metal element as in Embodiment 6, avery small amount of the metal element will remain in the island-likesemiconductor film. Of course, it is still possible to complete a TFTunder this state, but preferably better to remove at least the nickelelement that will remain in a channel-forming region. As a means ofremoving the catalyst element residue, there is a method of utilizing agettering action of phosphorus (P). A step in which phosphorus isselectively doped, heated, and gettered may be added. Nonetheless,without the addition of such step, the concentration of phosphorus (P)necessary for gettering is approximately the same level as theconcentration in the impurity region (n⁺) formed in FIG. 17B.Accordingly, by means of the heat treatment in the activation step shownin FIG. 17D, the catalyst element in the channel-forming region of then-channel type TFT and the p-channel type TFT can be gettered therefrom.

There are other means for removing the catalyst element without beingparticularly limited. For example, after forming the island-shapesemiconductor layer, heat treatment is performed on the crystallinesemiconductor film with a catalyst element residue at a temperaturebetween 800° C. and 1150° C. (preferably between 900° C. and 1000° C.)for 10 minutes to 4 hours (preferably between 30 minutes and 1 hour) inan oxygenous atmosphere to which 3 to 10 volume % of hydrogen chlorideis contained. Through this step, the nickel in the crystallinesemiconductor film becomes a volatile chloride compound (nickelchloride) and is eliminated in the treatment atmosphere during theoperation. In other words, it is possible to remove nickel by thegettering action of a halogen element.

A plural number of means may be used in combination to remove thecatalyst element. Also, gettering may be performed prior to theformation of the island-like semiconductor layer.

Embodiment 7

Referring to FIGS. 23A to 23D, an example of using another method ofcrystallization, substituting the crystallization step in Embodiment 5,is shown here in Embodiment 7.

First, the state of FIG. 23A is obtained in accordance with Embodiment5. Note that FIG. 23A corresponds to FIG. 15A.

First, an aqueous solution containing a catalyst element (nickel, inthis Embodiment) (aqueous nickel acetate solution) is applied to anamorphous silicon film by spin coating to form acatalyst-element-containing layer 1902 on the entire surface of anamorphous semiconductor film 1503 a. (FIG. 23B) Possible metal elementsother than nickel (Ni) that can be used here are elements such asgermanium (Ge), iron (Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt(Co), platinum (Pt), copper (Cu), and gold (Au).

The spin coating method is employed as a means of doping nickel inEmbodiment 7. However, other methods such as evaporation and sputteringmay be used for forming a thin film made of a catalyst element (nickelfilm in the case of Embodiment 7) on the amorphous semiconductor film.Though the example of forming the catalyst-element-containing layer 1902on the entire surface of the amorphous semiconductor film 1503 a isshown here in Embodiment 7, a mask may be formed to selectively form thecatalyst-element-containing layer.

Heat treatment is performed next at a temperature between 500° C. and650° C. (preferably between 550° C. and 600° C.) for a duration of 6hours to 16 hours (preferably between 8 and 14 hours). Consequently,crystallization is advanced and a crystalline semiconductor film(crystalline silicon film in Embodiment 7) 1902 is formed. (FIG. 23C) Inthe case of selectively forming the metal-element-containing layer, withan opening of the mask as the starting point, crystallization advancesin the direction substantially parallel (the direction indicated by anarrow) with the substrate. A crystalline silicon film that has uniform(even) crystal growth direction when viewed macroscopically is thusformed.

There are many defects included in the crystalline silicon filmcrystallized by the above method due to the low crystallizationtemperature, and there are cases in which it is insufficient for use asa semiconductor element material. Thus, in order to increase thecrystallinity of the crystalline silicon film, the film is irradiatedwith a laser beam using the laser irradiation method indicated in theembodiment mode of the present invention. A crystalline silicon film1903 having good crystallinity is thus formed. (FIG. 23D)

By performing the rest of the process in accordance with the steps afterFIG. 15C indicated in Embodiment 5, the structure shown in FIG. 21 canbe attained.

Note that similar to Embodiment 6, it is further preferable to removethe catalyst element that will remain at least from the channel-formingregion. Accordingly, it is also desirable that gettering be performed byusing the method indicated in Embodiment 5.

Embodiment 8

The structure of an active matrix type liquid crystal display deviceindicated in Embodiment 5 is explained using the perspective view ofFIG. 24. Note that in order to give correspondence with the diagrams ofFIGS. 15A to 20, common symbols are used for FIG. 24.

In FIG. 24, an active matrix substrate is structured by a display region1706, a scanning signal drive circuit 1704, and an image signal drivecircuit 1705 formed on a glass substrate 1501. A pixel TFT 1604 isprovided in the display region, and the drive circuits formed in theperiphery thereof are structured with CMOS circuit as a base. Thescanning signal drive circuit 1704 and the image signal drive circuit1705 are connected to the pixel TFT 1604 by a gate wiring 1548 and asource wiring 1554, respectively. Further, an FPC71 is connected to anexternal input terminal 72, and is connected via input wirings 73 and 74to the respective drive circuits. Reference symbol 1702 denotes anopposing substrate 1702.

Embodiment 9

An example of manufacturing an EL display (electroluminescence) usingthe present invention is explained in this embodiment.

FIG. 25A is a top view of an EL display device using the presentinvention. In FIG. 25A, reference numeral 4010 is a substrate, referencenumeral 4011 is a pixel portion, reference numeral 4012 is a sourcesignal side driver circuit, and reference numeral 4013 is a gate signalside driver circuit. Each driver circuits are connected to externalequipment, through an FPC 4017, via wirings 4014 to 4016.

A covering material 6000, a sealing material (also referred to as ahousing material) 7000, and an airtight sealing material (a secondsealing material) 7001 are formed so as to enclose at least the pixelportion, preferably the driver circuits and the pixel portion, at thispoint.

Further, FIG. 25B is a cross sectional structure of the EL displaydevice of the present invention. A driver circuit TFT 4022 (note that aCMOS circuit in which an n-channel. TFT and a p-channel TFT are combinedis shown in the figure here), a pixel portion TFT 4023 (note that onlyan EL driver TFT for controlling the current flowing to an EL element isshown here) are formed on a base film 4021 on a substrate 4010. The TFTsmay be formed using a known structure (a top gate structure or a bottomgate structure).

This invention can be applied to the driver circuit 4022 and the pixelportion TFT 4023.

After the driver circuit TFT 4022 and the pixel portion TFT 4023 arecompleted, a pixel electrode 4027 made from a transparent conductivefilm connected to a drain of pixel portion TFT 4023 is formed on aninterlayer insulating film (leveling film) 4026 made from a resinmaterial. An indium oxide and tin oxide compound (referred to as ITO) oran indium oxide and zinc oxide compound can be used as the transparentconducting film. An insulating film 4028 is formed after forming thepixel electrode 4027, and an open portion is formed on the pixelelectrode 4027.

An EL layer 4029 is formed next. The EL layer 4029 may be formed havinga lamination structure, or a single layer structure, by freely combiningknown EL materials (such as a hole injecting layer, a hole transportinglayer, a light emitting layer, an electron transporting layer, and anelectron injecting layer). A known technique may be used to determinewhich structure to use. Further, EL materials exist as low molecularweight materials and high molecular weight (polymer) materials.Evaporation is used when using a low molecular weight material, but itis possible to use easy methods such as spin coating, printing, and inkjet printing when a high molecular weight material is employed.

In this embodiment, the EL layer is formed by evaporation using a shadowmask. Color display becomes possible by forming emitting layers (a redcolor emitting layer, a green color emitting layer, and a blue coloremitting layer), capable of emitting light having different wavelengths,for each pixel using a shadow mask. In addition, methods such as amethod of combining a charge coupled layer (CCM) and color filters, anda method of combining a white color light emitting layer and colorfilters may also be used. Of course, the EL display device can also bemade to emit a single color of light.

After forming the EL layer 4029, a cathode 4030 is formed on the ELlayer. It is preferable to remove as much as possible any moisture oroxygen existing in the interface between the cathode 4030 and the ELlayer 4029. It is therefore necessary to use a method of depositing theEL layer 4029 and the cathode 4030 in an inert gas atmosphere or withina vacuum. The above film deposition becomes possible in this embodimentby using a multi-chamber method (cluster tool method) film depositionapparatus.

Note that a lamination structure of a LiF (lithium fluoride) film and anAl (aluminum) film is used in this embodiment as the cathode 4030.Specifically, a 1 nm thick LiF (lithium fluoride) film is formed byevaporation on the EL layer 4029, and a 300 nm thick aluminum film isformed on the LiF film. An MgAg electrode, a known cathode material, mayof course also be used. The wiring 4016 is then connected to the cathode4030 in a region denoted by reference numeral 4031. The wiring 4016 isan electric power supply line for imparting a predetermined voltage tothe cathode 4030, and is connected to the FPC 4017 through a conductingpaste material 4032.

In order to electrically connect the cathode 4030 and the wiring 4016 inthe region denoted by reference numeral 4031, it is necessary to form acontact hole in the interlayer insulating film 4026 and the insulatingfilm 4028. The contact holes may be formed at the time of etching theinterlayer insulating film 4026 (when forming a contact hole for thepixel electrode) and at the time of etching the insulating film 4028(when forming the opening portion before forming the EL layer). Further,when etching the insulating film 4028, etching may be performed all theway to the interlayer insulating film 4026 at one time. A good contacthole can be formed in this case, provided that the interlayer insulatingfilm 4026 and the insulating film 4028 are the same resin material.

A passivation film 6003, a filling material 6004, and the coveringmaterial 6000 are formed covering the surface of the EL element thusmade.

In addition, the sealing material 7000 is formed between the coveringmaterial 6000 and the substrate 4010, so as to surround the EL elementportion, and the airtight sealing material (the second sealing material)7001 is formed on the outside of the sealing material 7000.

The filling material 6004 functions as an adhesive for bonding thecovering material 6000 at this point. PVC (polyvinyl chloride), epoxyresin, silicone resin, PVB (polyvinyl butyral), and EVA (ethylene vinylacetate) can be used as the filling material 6004. If a drying agent isformed on the inside of the filling material 6004, then it can continueto maintain a moisture absorbing effect, which is preferable.

Further, spacers may be contained within the filling material 6004. Thespacers may be a powdered substance such as BaO, giving the spacersthemselves the ability to absorb moisture.

When using spacers, the passivation film 6003 can relieve the spacerpressure. Further, a film such as a resin film can be formed separatelyfrom the passivation film 6003 to relieve the spacer pressure.

Furthermore, a glass plate, an aluminum plate, a stainless steel plate,an FRP (fiberglass-reinforced plastic) plate, a PVF (polyvinyl fluoride)film, a Mylar film, a polyester film, and an acrylic film can be used asthe covering material 6000. Note that if PVB or EVA is used as thefilling material 6004, it is preferable to use a sheet with a structurein which several tens of μm of aluminum foil is sandwiched by a PVF filmor a Mylar film.

However, depending upon the light emission direction from the EL device(the light radiation direction), it is necessary for the coveringmaterial 6000 to have light transmitting characteristics.

Further, the wiring 4016 is electrically connected to the FPC 4017through a gap between the sealing material 7000, the sealing material7001 and the substrate 4010. Note that although an explanation of thewiring 4016 has been made here, the wirings 4014 and 4015 are alsoelectrically connected to the FPC 4017 by similarly passing underneaththe sealing material 7001 and sealing material 7000.

Embodiment 10

In this embodiment, an example of manufacturing an EL display devicehaving a structure which differs from that of Embodiment 9 is explainedusing FIGS. 26A and 26B. Parts having the same reference numerals asthose of FIGS. 25A and 25B indicate the same portions, and therefore anexplanation of those parts is omitted.

FIG. 26A is a top view of an EL display device of this embodiment, andFIG. 26B shows a cross sectional diagram in which FIG. 26A is cut alongthe line A-A′.

In accordance with Embodiment 9, manufacturing is performed through thestep of forming the passivation film 6003 covering the EL element.

In addition, the filling material 6004 is formed so as to cover the ELelement. The filling material 6004 also-functions as an adhesive forbonding the covering material 6000. PVC (polyvinyl chloride), epoxyresin, silicone resin, PVB (polyvinyl butyral), and EVA (ethylene vinylacetate) can be used as the filling material 6004. If a drying agent isprovided on the inside of the filling material 6004, then it cancontinue to maintain a moisture absorbing effect, which is preferable.

Further, spacers may be contained within the filling material 6004. Thespacers may be a powdered substance such as BaO, giving the spacersthemselves the ability to absorb moisture.

When using spacers, the passivation film 6003 can relieve the spacerpressure. Further, a film such as a resin film can be formed separatelyfrom the passivation film 6003 to relieve the spacer pressure.

Furthermore, a glass plate, an aluminum plate, a stainless steel plate,an FRP (fiberglass-reinforced plastic) plate, a PVF (polyvinyl fluoride)film, a Mylar film, a polyester film, and an acrylic film can be used asthe covering material 6000. Note that if PVB or EVA is used as thefiller material 6004, it is preferable to use a sheet with a structurein which several tens of μm of aluminum foil is sandwiched by a PVF filmor a Mylar film.

However, depending upon the light emission direction from the EL device(the light radiation direction), it is necessary for the coveringmaterial 6000 to have light transmitting characteristics.

After bonding the covering material 6000 using the filling material6004, the frame material 6001 is attached so as to cover the lateralsurfaces (exposed surfaces) of the filling material 6004. The framematerial 6001 is bonded by the sealing material (which functions as anadhesive) 6002. It is preferable to use a light hardening resin as thesealing material 6002 at this point, but provided that the heatresistance characteristics of the EL layer permit, a thermal hardeningresin may also be used. Note that it is preferable that the sealingmaterial 6002 be a material which, as much as possible, does nottransmit moisture and oxygen. Further, a drying agent may also be addedto an inside portion of the sealing material 6002.

The wiring 4016 is electrically connected to the FPC 4017 through a gapbetween the sealing material 6002 and the substrate 4010. Note thatalthough an explanation of the wiring 4016 has been made here, thewirings 4014 and 4015 are also electrically connected to the FPC 4017 bysimilarly passing underneath the sealing material 6002.

Embodiment 11

The present invention can be applied to the EL display panel with thestructure of Embodiments 9 and 10. FIG. 27 shows a more detailedcross-sectional structure of the pixel portion. FIG. 28A shows a topview thereof, and FIG. 28B shows a circuit diagram thereof. In FIGS. 27,28A, and 28B, the same components are denoted with the same referencenumerals.

In FIG. 27, a TFT 3502 for switching provided on a substrate 3501 isformed by using the NTFT according to the present invention. (SeeEmbodiments 1 to 8) In this embodiment, the TFT has a double-gatestructure. Since there is no substantial difference in its structure andproduction process, its description will be omitted. Due to thedouble-gate structure, there is an advantage in that substantially twoTFTs are connected in series to reduce an OFF current value. In thisembodiment, the TFT has a double-gate structure; however, it may have asingle gate structure, a triple gate structure, or a multi-gatestructure having 4 or more gates. Alternatively, PTFT according to thepresent invention may be used.

A current controlling TFT 3503 is formed by using the NTFT of thepresent invention. A drain wiring 35 of the switching TFT 3502 iselectrically connected to a gate electrode 37 of the current controllingTFT by a wiring 36. Furthermore, a wiring 38 is a gate wiringelectrically connected to gate electrodes 39 a and 39 b of the switchingTFT 3502.

At this time, it is very important that the current control TFT 3503 hasa structure according to the present invention. The current controllingTFT functions for controlling the amount of a current flowing through anEL element, so that the TFT is likely to be degraded by heat and hotcarriers due to a large amount of current flown therethrough. Therefore,the structure of the present invention is very effective, in which anLDD region is provided on the drain side of the current controlling TFTso as to overlap the gate electrode via the gate insulating film.

Furthermore, in this embodiment, the current controlling TFT 3503 has asingle gate structure. However, it may have a multi-gate structure inwhich a plurality of TFTs are connected in series. Furthermore, it mayalso be possible that a plurality of TFTs are connected in parallel tosubstantially divide a channel formation region into a plurality ofparts, so as to conduct highly efficient heat release. Such a structureis effective for preventing degradation due to heat.

As shown in FIG. 28A, a line to be the gate electrode 37 of the currentcontrolling TFT 3503 overlaps a drain wiring 40 of the currentcontrolling TFT 3503 via an insulating film in a region 3504. In theregion 3504, a capacitor is formed.

The capacitor 3504 functions for holding a voltage applied to a gate ofthe current controlling TFT 3503. The drain line 40 is connected to acurrent supply line (power source line) 3506 so as to be always suppliedwith a constant voltage.

A first passivation film 41 is provided on the switching TFT 3502 andthe current controlling TFT 3503, and a flattening film 42 that is madeof a resin insulating film is formed thereon. It is very important toflatten the step difference due to TFTs by using the flattening film 42.The step difference may cause a light-emitting defect because the ELlayer to be formed later is very thin. Thus, it is desirable to flattenthe step difference so that the EL layer is formed on a flat surfacebefore forming a pixel electrode.

Reference numeral 43 denotes a pixel electrode (cathode of an ELelement) that is made of a conductive film with high reflectivity and iselectrically connected to the drain of the current controlling TFT 3503.As the pixel electrode 43, a low resistant conductive film such as analuminum alloy film, a copper alloy film, and a silver alloy film, or alayered structure thereof can be preferably used. Needless to say, alayered structure with other conductive films may also be used.

A light-emitting layer 45 is formed in a groove (corresponding to apixel) formed by banks 44 a and 44 b made of an insulating film(preferably resin). Herein, only one pixel is shown; however,light-emitting layers corresponding to each color ® (red), G (green),and B (blue)) may be formed. As an organic EL material for thelight-emitting layer, a π-conjugate polymer material is used. Examplesof the polymer material include polyparaphenylene vinylene (PPV),polyvinyl carbazole (PVK), and polyfluorene.

There are various types of PPV organic EL materials. For example,materials as described in “H. Shenk, Becker, O. Gelsen, E. Kluge, W.Kreuder and H. Spreitzer, “Polymers for Light Emitting Diodes”, EuroDisplay, Proceedings, 1999, pp. 33-37” and Japanese Laid-OpenPublication No. 10-92576 can be used.

More specifically, as a light-emitting layer emitting red light,cyanopolyphenylene vinylene may be used. As a light-emitting layeremitting green light, polyphenylene vinylene may be used. As alight-emitting layer emitting blue light, polyphenylene vinylene orpolyalkyl phenylene may be used. The film thickness may be prescribed tobe 30 to 150 nm (preferably 40 to 100 nm).

The above-mentioned organic EL materials are merely examples for use asa light-emitting layer. The present invention is not limited thereto. Alight-emitting layer, a charge-transporting layer, or a charge injectionlayer may be appropriately combined to form an EL layer (for lightemitting and moving carriers therefor).

For example, in this embodiment, the case where a polymer material isused for the light-emitting layer has been described. However, a lowmolecular-weight organic EL material may be used. Furthermore, aninorganic material such as silicon carbide can also be used for acharge-transporting layer and a charge injection layer. As these organicEL materials and inorganic materials, known materials can be used.

In this embodiment, an EL layer with a layered structure is used, inwhich a hole injection layer 46 made of PEDOT (polythiophene) or PAni(polyaniline) is provided on the light-emitting layer 45. An anode 47made of a transparent conductive film is provided on the hole injectionlayer 46. In this embodiment, light generated by the light-emittinglayer 45 is irradiated to the upper surface (toward TFTs), so that theanode 47 must be transparent to light. As a transparent conductive film,a compound of indium oxide and tin oxide, and a compound of indium oxideand zinc oxide can be used. The conductive film is formed after formingthe light-emitting layer and the hole injection layer with low heatresistance, so that the conductive film that can be formed at a possiblylow temperature is preferably used.

When the anode 47 is formed, the EL element 3505 is completed. The ELelement 3505 refers to a capacitor composed of the pixel electrode(cathode) 43, the light-emitting layer 45, the hole injection layer 46,and the anode 47. As show in FIG. 28A, the pixel electrode 43substantially corresponds to the entire area of a pixel. Therefore, theentire pixel functions as an EL element. Thus, a light image displaywith very high light use efficiency can be performed.

In this embodiment, a second passivation film 48 is further formed onthe anode 47. As the second passivation film 48, a silicon nitride filmor a silicon nitride oxide film is preferably used. The purpose of thepassivation film 48 is to prevent the EL element from being exposed tothe outside. That is, the passivation film 48 protects an organic ELmaterial from degradation due to oxidation, and suppresses the releaseof gas from the organic EL material. Because of this, the reliability ofthe EL display device is enhanced.

As described above, the EL display panel of the present invention has apixel portion made of a pixel with a structure as shown in FIG. 27, andincludes a switching TFT having a sufficiently low OFF current value anda current controlling TFT that is strong to the injection of hotcarriers. Thus, an EL display panel is obtained, which has highreliability and is capable of displaying a satisfactory image.

This embodiment can be realized by being appropriately combined with thestructures of Embodiments 1 to 8. Furthermore, it is effective to usethe EL display panel of this embodiment as a display portion ofelectronic equipment.

Embodiment 12

In this embodiment, referring to FIG. 29, the case will be describedwhere the structure of the EL element 3505 is reversed in the pixelportion described in Embodiment 11. The difference from the structureshown in FIG. 27 lies only in the EL element and the current controllingTFT, so that the description of the other parts will be omitted.

In FIG. 29, a current controlling TFT 3503 is formed of a PTFT accordingto the present invention. Regarding the production process, Embodiments1 to 8 should be referred to.

In this embodiment, a transparent conductive film is used as a pixelelectrode (anode) 50. More specifically, a conductive film made of acompound of indium oxide and zinc oxide is used. Needless to say, aconductive film made of a compound of indium oxide and tin oxide may beused.

After banks 51 a and 51 b made of an insulating film are formed, alight-emitting layer 52 made of polyvinyl carbazole is formed by coatingof a solution. On the light-emitting layer 52, an electron injectionlayer 53 made of potassium acetyl acetonate (acacK), and a cathode 54made of an aluminum alloy are formed. In this case, the cathode 54functions as a passivation film. Thus, an EL element 3701 is formed.

In this embodiment, light generated by the light-emitting layer 52 isirradiated toward the substrate on which a TFT is formed as representedby an arrow.

This embodiment can be realized by being appropriately combined with thestructures of Embodiments 1 to 8. Furthermore, it is effective to usethe EL display panel of this embodiment as a display portion ofelectronic equipment.

Embodiment 13

In this embodiment, referring to FIGS. 30A to 30C, the case will bedescribed where a pixel having a structure different from that of thecircuit diagram shown in FIG. 28B is used. Reference numeral 3801denotes a source line of a switching TFT 3802, 3803 denotes a gatewiring of the switching TFT 3802, 3804 denotes a current controllingTFT, 3805 denotes a capacitor, 3806 and 3808 denote current supplylines, and 3807 denotes an EL element.

FIG. 30A shows the case where two pixels share the current supply line3806. More specifically, two pixels are formed so as to be axisymmetricwith respect to the current supply line 3806. In this case, the numberof power supply lines can be reduced, so that the pixel portion isallowed to have a higher definition.

Furthermore, FIG. 30B shows the case where the current supply line 3808and the gate line 3803 are provided in parallel. In FIG. 30B, althoughthe current supply line 3808 does not overlap the gate wiring 3803, ifboth lines are formed on different layers, they can be provided so as tooverlap each other via an insulating film. In this case, the currentsupply line 3808 and the gate line 3803 can share an occupied area, sothat a pixel portion is allowed to have higher definition.

Furthermore, FIG. 30C shows the case where the current supply line 3808and gate wiring 3803 are provided in parallel in the same way as in FIG.30B, and two pixels are formed so as to be axisymmetric with respect tothe current supply line 3808. It is also effective to provide thecurrent supply line 3808 so as to overlap one of the gate wiring 3803.In this case, the number of the power supply lines can be reduced, sothat a pixel portion is allowed to have higher definition.

This embodiment can be realized by being appropriately combined with thestructures of Embodiments 1 to 10. Furthermore, it is effective to usethe EL display panel of this embodiment as a display portion ofelectronic equipment.

Embodiment 14

In FIGS. 28A and 28B shown in Embodiment 11, the capacitor 3504 isprovided so as to hold a voltage applied to a gate of the currentcontrolling TFT 3503. However, the capacitor 3504 can be omitted. InEmbodiment 11, since the NTFT according to the present invention asshown in Embodiment 1 to 8 is used as the current controlling TFT 3503,the TFT 3503 has an LDD region provided so as to overlap a gateelectrode via a gate insulating film. In this region, a parasiticcapacitor called a gate capacitor is generally formed. This embodimentis characterized in that the parasitic capacitor is used in place of thecapacitor 3504.

The capacitance of the parasitic capacitor is varied depending upon thearea in which the above-mentioned gate electrode overlaps the LDDregion. Therefore, the capacitance is determined by the length of theLDD region included in the region positively.

Similarly, in FIGS. 30A, 30B, and 30C, the capacitor 3805 can also beomitted.

This embodiment can be realized by being appropriately combined with thestructures of Embodiments 1 to 13. Furthermore, it is effective to usean EL display panel having a pixel structure of this embodiment as adisplay portion of electronic equipment.

Embodiment 15

The CMOS circuit and the pixel portion formed by implementing thepresent invention can be used in various electro-optical devices (activematrix type liquid crystal display device, active matrix EL displaydevice, and active matrix EC display). That is, the present inventioncan be implemented in all electronic equipment that incorporate theseelectro-optical devices as a display portion.

The following can be given as such electronic equipment: a video camera,a digital camera, a projector (a rear type or a front type), a headmount display (goggle type display), a car navigation system, a carstereo, a personal computer, a portable information terminal (such as amobile computer, a cellular phone, and an electronic book) etc. Someexamples of these are shown in FIG. 31, FIG. 32 and FIG. 33.

FIG. 31A shows a personal computer that is comprised of a main body2001, an image input portion 2002, a display portion 2003, and akeyboard 2004. The present invention can be applied to the image inputportion 2002, the display portion 2003 and the other signal controlcircuit.

FIG. 31B shows a video camera that is comprised of a main body 2101, adisplay portion 2102, an audio input portion 2103, operation switches2104, a battery 2105, and an image receiving portion 2106. The presentinvention can be applied to the display portion 2102, and other signalcontrol circuit.

FIG. 31C shows a mobile computer that is composed of a main body 2201, acamera portion 2202, an image receiving portion 2203, operation switches2204, and a display portion 2205. The present invention can be appliedto the display portion 2205 and other signal control circuit.

FIG. 31D shows a goggle type display that is comprised of a main body2301, display portions 2302, and arm portions 2303. The presentinvention can be applied to the display portion 2302 and other signalcontrol circuit.

FIG. 31E shows a player which uses a recording medium in which a programis stored (hereinafter referred to as a recording medium) and which iscomprised of a main body 2401, a display portion 2402, speaker portions2403, a recording medium 2404, and operation switches 2405. A DVD(Digital Versatile Disc), a CD or the like is used as the recordingmedium to enable the player to appreciate music and the movies, and playa game or the Internet. The present invention can be applied to thedisplay portion 2402 and other signal control circuit.

FIG. 31F shows a digital camera that is comprised of a main body 2501, adisplay portion 2502, an eye-piece portion 2503, operation switches2504, and an image receiving portion (not shown in the figure). Thepresent invention can be applied to the display portion 2502 and othersignal control circuit.

FIG. 32A shows a front type projector that is comprised of a projectionunit 2601, a screen 2602, and the like. The present invention can beapplied to a liquid crystal display device 2808 which is a partstructuring the projection unit 2601 and other signal control circuit.

FIG. 32B shows a rear type projector that is comprised of a main body2701, a projection unit 2702, a mirror 2703, a screen 2704, and thelike. The present invention can be applied to the liquid crystal displaydevice 2808 which is a part structuring the projection unit 2702 andother signal control circuit.

Illustrated in FIG. 32C is an example of the structure of the projectionunits 2601 and 2702 that are shown in FIGS. 32A and 32B, respectively.Each of the projection units 2601 and 2702 is comprised of a lightsource optical system 2801, mirrors 2802 and 2804 to 2806, dichroicmirrors 2803, a prism 2807, liquid crystal display devices 2808, phasedifference plates 2809, and a projection optical system 2810. Theprojection optical system 2810 is constructed of an optical systemincluding projection lenses. An example of a three plate system is shownin the present embodiment, but there are no special limitations. Forinstance, an optical system of single plate system is acceptable.Further, the operator may suitably set optical systems such as opticallenses, polarizing film, film to regulate the phase difference, IR film,within the optical path shown by the arrows in FIG. 32C.

In addition, FIG. 32D shows an example of the structure of the lightsource optical system 2801 of FIG. 32C. In the present embodiment, thelight source optical system 2801 is composed of a reflector 2811, alight source 2812, a lens array 2813 and 2814, a polarizing conversionelement 2815, and a condenser lens 2816. Note that the light sourceoptical system shown in FIG. 32D is an example, and it is not limited tothe illustrated structure. For example, the operator may suitably setoptical systems such as optical lenses, polarizing film, film toregulate the phase difference, and IR film.

The projector illustrated in FIG. 32, show the electro optical device oftransparent type but the example of the electro optical device ofreflection type and the EL display device.

FIG. 33A shows a cellular phone that is comprised of a main body 2901,an audio output portion 2902, an audio input portion 2903, a displayportion 2904, an operation switches 2905 and an antenna 2906 etc. Thepresent invention can be applied to the audio output portion 2902, theaudio input portion 2903, the display portion 2904 and other signalcontrol circuit.

FIG. 33B shows a mobile book (electronic book) that is comprised of amain body 3001, a display portion 3002, 3003, a recording medium 3004,an operation switches 3005 and a antenna 3006 etc. The present inventioncan be applied to the display portion 3002, 3003 and other signalcontrol circuit.

FIG. 33C shows a display that is comprised of a main body 3101, asupport stand 3102 and display portion 3103 etc. The present inventioncan be applied to the display portion 3103. They are especiallyadvantageous for cases in which the screen is made large, and isfavorable for displays having a diagonal greater than or equal to 10inches (especially one which is greater than or equal to 30 inches).

Thus, the application range for the present invention is extremely wide,and it may be applied to electronic equipment in all fields. Further,the electronic equipment of this Embodiment can be realized with acomposition that uses any combination of Embodiments 1 to 14.

The provision of a high cost performance laser irradiation process canbe attained by the laser irradiation apparatus of the present invention.In addition, laser beams having a higher uniformity can be obtainedthrough the present invention. The laser irradiation apparatus providedby the present invention can be utilized in processes such as thecrystallization process of the non-single crystal silicon film.

1. An apparatus for irradiating a laser beam comprising: a laseroscillator for emitting a plurality of laser beams having differentwavelengths from each other; an optical system for uniforming an energydistribution of each of said plurality of laser beams by synthesizingeach of said plurality of laser beams having different wavelengths fromeach other into a laser beam having a square or rectangularcross-section on an object to be irradiated; and a stage over which theobject to be irradiated is disposed.
 2. An apparatus according to claim1 wherein said laser oscillator comprises a YAG laser.
 3. An apparatusaccording to claim 1 wherein said laser oscillator comprises azigzag-slab-style YAG laser.
 4. An apparatus according to claim 1wherein said object is a non-single crystal semiconductor filmcomprising silicon.
 5. An apparatus according to claim 1 wherein saidplurality of laser beams having different wavelengths from each othercomprise second and third harmonics of a YAG laser beam.
 6. An apparatusaccording to claim 1 wherein said plurality of laser beams havingdifferent wavelengths from each other comprise second and fourthharmonics of a YAG laser beam.
 7. An apparatus according to claim 1wherein said plurality of laser beams having different wavelengths fromeach other comprise third and fourth harmonics of a YAG laser beam. 8.An apparatus according to claim 1 wherein each of said plurality oflaser beams having different wavelengths from each other has awavelength of 600 nm or less.
 9. An apparatus according to claim 1further comprising: a load/unload chamber; a transfer chamber; a robotarm; and a laser irradiation chamber.
 10. An apparatus for irradiating alaser beam according to claim 1, wherein the optical system comprises afirst optical system and a second optical system.
 11. An apparatus forirradiating a laser beam according to claim 10, wherein each of thefirst optical system and the second optical system comprises a firstcylindrical lens array, a second cylindrical lens array, a firstcylindrical lens, a second cylindrical lens and a third cylindricallens.
 12. An apparatus for irradiating a laser beam with a linearcross-section on an object to be irradiated, said apparatus comprising:a laser oscillator for emitting a plurality of laser beams havingdifferent wavelengths from each other; an optical system for uniformingan energy distribution of each of said plurality of laser beams bysynthesizing each of said plurality of laser beams having differentwavelengths from each other into a laser beam having a linearcross-section; and means for moving the object to be irradiatedrelatively to said plurality of laser beams.
 13. An apparatus accordingto claim 12 wherein said laser oscillator comprises a YAG laser.
 14. Anapparatus according to claim 12 wherein said laser oscillator comprisesa zigzag-slab-style YAG laser.
 15. An apparatus according to claim 12wherein said object is a non-single crystal semiconductor filmcomprising silicon.
 16. An apparatus according to claim 12 wherein saidplurality of laser beams having different wavelengths from each othercomprise second and third harmonics of a YAG laser beam.
 17. Anapparatus according to claim 12 wherein said plurality of laser beamshaving different wavelengths from each other comprise second and fourthharmonics of a YAG laser beam.
 18. An apparatus according to claim 12wherein said plurality of laser beams having different wavelengths fromeach other comprise third and fourth harmonics of a YAG laser beam. 19.An apparatus according to claim 12 wherein each of said plurality oflaser beams having different wavelengths from each other has awavelength of 600 nm or less.
 20. An apparatus according to claim 12further comprising: a load/unload chamber; a transfer chamber; a robotarm; and a laser irradiation chamber.
 21. An apparatus for irradiating alaser beam according to claim 12, wherein the optical system comprises afirst optical system and a second optical system.
 22. An apparatus forirradiating a laser beam according to claim 21, wherein each of thefirst optical system and the second optical system comprises a firstcylindrical lens array, a second cylindrical lens array, a firstcylindrical lens, a second cylindrical lens and a third cylindricallens.
 23. An apparatus for irradiating a laser beam according to claim12, wherein the means for moving the object is a ball screw type or alinear motor.
 24. An apparatus for irradiating a laser beam with alinear cross-section on an object to be irradiated, said apparatuscomprising: a laser oscillator for emitting a plurality of laser beamshaving different wavelengths from each other; an optical system foruniforming an energy distribution of each of said plurality of laserbeams by synthesizing each of said plurality of laser beams havingdifferent wavelengths from each other into a laser beam having a linearcross-section; and a stage over which the object to be irradiated isdisposed.
 25. An apparatus according to claim 24 wherein said laseroscillator comprises a YAG laser.
 26. An apparatus according to claim 24wherein said laser oscillator comprises a zigzag-slab-style YAG laser.27. An apparatus according to claim 24 wherein said object is anon-single crystal semiconductor film comprising silicon.
 28. Anapparatus according to claim 24 wherein said plurality of laser beamshaving different wavelengths from each other comprise second and thirdharmonics of a YAG laser beam.
 29. An apparatus according to claim 24wherein said plurality of laser beams having different wavelengths fromeach other comprise second and fourth harmonics of a YAG laser beam. 30.An apparatus according to claim 24 wherein said plurality of laser beamshaving different wavelengths from each other comprise third and fourthharmonics of a YAG laser beam.
 31. An apparatus according to claim 24wherein each of said plurality of laser beams having differentwavelengths from each other has a wavelength of 600 nm or less.
 32. Anapparatus according to claim 24 further comprising: a load/unloadchamber; a transfer chamber; a robot arm; and a laser irradiationchamber.
 33. An apparatus for irradiating a laser beam according toclaim 24, wherein the optical system comprises a first optical systemand a second optical system.
 34. An apparatus for irradiating a laserbeam according to claim 33, wherein each of the first optical system andthe second optical system comprises a first cylindrical lens array, asecond cylindrical lens array, a first cylindrical lens, a secondcylindrical lens and a third cylindrical lens.